The 3 Best Batteries For An Off-Grid Energy System

It’s the question that anyone using alternative energy inevitably asks at some point… What are the best batteries for an off-grid energy system?

Prolong The Life Of Lithium-ion, Laptop, and Cell Phone Batteries

Some of the most expensive batteries to replace are cell phone and laptop batteries – also known as Lithium-Ion (Li-ion) batteries. A lot of people don’t realize that poor care and poor charging practices dramatically decrease the battery life of their lithium-ion batteries.

7 Ways To Prolong The Life Of Deep Cycle Lead-Acid Batteries

If you use an off-grid alternative energy system, you will need a battery bank with deep cycle batteries. The most common deep cycle batteries used in off-grid energy systems are (deep cycle) lead-acid batteries

8 Simple Tips and Tricks To Extend The Life Of Your Car Battery

Your car battery should last about 3 to 5 years… But many people find that they have to change their car battery every 1 to 2 years. Why is this?

What Is An Equalizing Charge, Why Is It Needed, And How to Apply One To a Lead Acid Battery

Applying an equalizing charge to your lead-acid batteries will help them charge better and last longer.



10/20/2022

the EZ Battery Reconditioning program (WATCH VIDEO)


Most people spend $15,000+ on batteries over their lifetime and this number continues to grow each day because people are using more and more batteries, and batteries continue to get more expensive. But our course helps reduce this huge cost because people can reuse old (reconditioned) batteries instead! We also teach people all about proper battery maintenance so their new batteries last much longer.

Do This To Bring Any Old Battery Back To Life - Just Like New!

4/14/2017

7 Signs Your Car Battery Is About To Die And Needs To Be Replaced (or reconditioned)


Without a battery, your car simply isn’t functional. One of the most inconvenient things in life is when your car battery suddenly dies unexpectedly! This can delay you to work or make you miss an important appointment!

But the good news is… there are several ways to know if your car battery is on the verge of dying and needs to be replaced. And in this article we will go over 7 signs your car battery is about to die and needs to be replaced or reconditioned.


Something to note before we begin...

Before we discuss these 7 critical signs, it's important to note that when experiencing problems with your car battery, be sure to check the battery connections and cables first because sometimes a faulty connection can appear to be a larger problem.

1) Slow Cranking

When turning the key, if your car turns over for longer than normal or takes a while to “catch,” it often is because the battery charge is low. While the starter can be the culprit, most of the time the battery is to blame. If this is happening regularly, it’s a good sign your car battery is going bad and it may be time to replace your battery or recondition it.


2) Check Engine Light/Battery Warning Light

The check engine light is always a good indication of something off with your vehicle. The battery power being weak will trip the check engine light. If your check engine light is on, be sure to check the battery power level.

Additionally, newer cars have a battery light, similar to the check engine light. This will only light up if there’s an issue with the battery.






3) Age

A car battery lifespan, in perfect conditions, is about five years (but can be much longer if you use our battery reconditioning course). If your battery is coming up on the five to six year mark it’s time to start looking for a replacement or recondition it to give the battery a new life.


4) Electrical Component Issues

One sure sign that your battery is beginning to fade is if electrical components are struggling to operate (such as lights, windshield wipers, power locks, and windows).

5) Swollen Battery Case

If you look under the hood and your battery case looks swollen, bloated, or malformed; it is a sign that temperature has affected the chemical components of the battery, shortening the lifespan.


6) Smell

If you smell sulfur or rotten eggs under your hood, this is often a symptom of leaking battery acid. This can damage other engine components if not addressed quickly. If you notice this, you can either bring your battery into a shop and have them look at it or you can use our reconditioning steps and do it yourself.


7) Multiple Jump starts Needed

If you’re having to jump your battery to get your car started more than three times a week, it’s time to replace the battery or recondition it. Excessive jumping can also damage other systems, so it’s best to get the battery replaced or to fix the battery yourself.

Regular maintenance is important to extend the life of your car battery (and also your vehicle). And if your car battery is showing any of these 7 signs, you know that your battery should be replaced or reconditioned before your car no longer runs.

And if you want to take it a step further… you can learn how to double or even triple the life of your car battery by watching this presentation now.



restore dead car battery

4/12/2017

What Is An Equalizing Charge, Why Is It Needed, And How to Apply One To a Lead Acid Battery


Applying an equalizing charge to your lead-acid batteries will help them charge better and last longer.

So whether you are a battery reconditioning expert or a rookie, it is essential that you know what an equalizing charge is and how to apply one to a lead-acid battery, so you can get the most out of your battery.

This simple technique is something that needs to be done on a somewhat regular schedule, and is basically the controlled overcharging of the battery.

So in this article I will tell you:

- Why an equalizing charge is needed

- What problems an equalizing charge fixes in your lead-acid batteries

- Two different ways to apply an equalizing charge

- Which types of lead-acid batteries you should not apply an equalizing charge to

- And how often you should apply an equalizing charge to your lead-acid batteries


Why Is An Equalizing Charge Needed?

An equalizing charge is needed because lead-acid batteries have sulfation issues that prevent proper charging.

Sulfation takes place because small sulfate crystals form when a lead acid battery is in use. This is normal and not harmful; however, when the battery is only partially charged for a prolonged period, these sulfate crystals turn into stable crystalline and buildup on the battery’s negative plates.

When this takes place, it prevents the battery from taking on a full charge.

Additionally, an equalizing charge is needed for a second reason. Over time, cells in a lead-acid battery will become more and more unbalanced, with some cells overcharged and some undercharged.

But an equalizing charge will correct these sulfation and unbalanced cell issues.


Things that cause Sulfation in Lead-Acid Batteries:

- When batteries are undercharged, they develop sulfation as a result.

- Normal recharging of a deep cycle battery with a constant charge can also cause sulfation.

So some degree of sulfation is inevitable in lead-acid batteries.


Why Does An Equalizing Charge Help?

When you perform an equalizing charge you will break up the crystalline on the battery’s plates and allow the sulfate to re-mix with the sulfuric acid.

Additionally, an equalizing charge will ensure the cells operate with the same level of charge rather than having some cells that are overcharged and some that are undercharged.

Both of these factors will help the battery charge and perform better, as well as last longer.


How Is An Equalizing Charge Applied To The Battery?

The Easy Way (Use Automatic Equalizing Mode On A Battery Charger):

The easiest way to apply an equalizing charge to a lead-acid battery is to use a high-quality battery charger that has an automatic equalizing mode. Many new battery chargers have this setting so finding a quality charger that can equalize your battery shouldn’t be a problem.

If you do use a charger that has an equalizing mode, just make sure you leave your battery connected and powered up long enough to complete the equalization.





The Manual Way To Apply An Equalizing Charge To A Lead-Acid Battery:

If you do not want to buy a charger that does an equalizing charge automatically or if you just want to manually apply an equalizing charge yourself, you can follow these steps:

Step 1) Get out your battery charger (i.e. one does not have an equalizing mode).

Step 2) Get out your lead-acid battery and ensure that the battery is a FLA (flooded lead-acid) battery.

*IMPORTANT: Applying an equalizing charge to other kinds of batteries may cause damage and is not recommended. This includes SLA (sealed lead-acid) batteries like AGM (absorbed glass mat) and Gel batteries.

Step 3) Remove all electrical connections to the battery.

Step 4) Connect the battery to the charger.

Step 5) Charge the battery until it has reached a normal full charge.

Step 6) At this stage the charge is usually automatically terminated by the charger.

Step 7) If your charger does not have an equalizing mode, you should now restart the charger once the initial full charge has been reached. Restarting the charger can be done by disconnecting AC power and reconnecting it. This process will extend the charge time for the battery by 1-3 hours.

Step 8) Gassing and bubbling of the electrolytes and other side effects will occur as a result of correct equalizing.

Step 9) Make sure you take specific gravity readings and the true state of the battery’s charge every hour during this process using a temperature compensating hydrometer.

*note: we show how to do this in our Battery Reconditioning course

Step 10) Make sure you also replace any water that is lost in the equalizing process.

*note: we show how to do this in our Battery Reconditioning course

Step 11) Check to see if the equalizing process has been completed. You will know if this has happened when the specific gravity values are no longer increasing during the gassing stage.

                   *note: If the charger ends the process automatically, before the equalizing charge has                              been completed and before the gravity readings are constant, then restart the charger                            and continue the equalizing until the gravity readings are constant.


How Often Should You Apply An Equalizing Charge To The Battery?

Different battery manufacturers recommend different intervals for when to apply an equalizing charge.

The most common interval is monthly. But other manufacturers recommend once every 6 months, while others recommend every 10 or 12 cycles.

So check with the battery manufacturer to see what they recommend and then follow that interval.

Additionally, make sure you are adding water to the battery every month and every time you perform an equalizing charge.


Is There More That Can Be Done To Maximize A Lead-Acid Battery’s Life?

Performing these equalizing charges and adding water regularly to a flooded lead-acid battery will extend the life of the battery and help it perform optimally.

But there’s a way you can extend the life of the battery even more and even bring a dead lead-acid battery back to life again…

Our EZ Battery Reconditioning course shows you exactly how to do this step-by-step.

The simple method we show you how to do in our program is quick, easy to do, and doesn’t require advanced tools or equipment.

So if you want to take it to the next level and bring any lead-acid battery back to life again …as well as  many other kinds of batteries, check out the new presentation I just put up to learn more.



lead acid battery repair

4/10/2017

8 Simple Tips & Tricks To Extend The Life Of Your Car Battery


Your car battery should last about 3 to 5 years…

But many people find that they have to change their car battery every 1 to 2 years.

Why is this?

And what can you do to prolong your car’s battery life?

Well… That’s what we’ll discuss in this article.

We’ll show you why car batteries die early …and what you can do to prevent this from happening.

We’ll also give you 8 simple tips and tricks to maximize the lifespan of your car’s 12 volt battery.

The tips we’ll teach you in this article will be simple to do …and anybody will be able to do these (even if you know nothing about cars or car batteries).

So let’s get started!…


First, You Should Know That Every Car Battery’s Lifespan Has A Limit (but most people kill their battery well before it’s time)

First, every car battery has a limit to its lifespan.

Even if you take care of your car battery perfectly …it will still die one day.

This set lifespan is called the battery’s “Calendar Life” and it’s completely independent of how many times the battery has been charged or discharged.

Once a battery reaches the end of its “Calendar Life” it will become unusable.

But most car batteries never make it their full “Calendar Life”…

Instead, they die early because of poor maintenance and care …which you can do something about.


A Little Background About Lead Acid Batteries Before Our 8 Battery Tips and Tricks…

Lead acid batteries are the oldest, most dependable, and most widely used type of rechargeable battery in the world.

Lead Acid Batteries have three life phases – formatting, peak, and decline.

- Formatting is when the battery is new and needs to be used gently.

- Peak is the ideal performance phase, which we seek to maintain for as long as possible.

- Decline is a slow process, but one that gradually ends in the termination of the battery.

Batteries in decline can still be used for quite a while, but must be watched.

Around this time, you can either recondition the battery or keep a close eye on it and try to replace it before a problem arises (like being unable to start your car for work).


8 Simple Tips To Prolong The Life Of Your Car’s Lead Acid Battery

Tip 1: Do a monthly inspection of the battery terminals to make sure they are clean and corrosion free

One of the first problems most people have with their car battery is the build-up of corrosion around the terminals.

Corrosion destroys the connection between the battery and the vehicle and many batteries are replaced due to too much corrosive build up.


But often times, this can be easily treated by simply pouring a small amount of Cola or a DIY anti-corrosion paste (one part water to three parts baking soda) over the corroded areas.

The acid in the Cola or the alkaline properties in the DIY anti-corrosion paste will eat the corrosion away.

After the corrosion is gone, use a clean damp rag or sponge to clean up the remaining residue and moisture.

Be sure to let it dry, then rub some petroleum jelly on the terminals to prevent future corrosion.

*note: see our safety tips at the end of this article before disconnecting/re-connecting your battery.


Tip 2: Do not operate any car accessories (radio, lights, or electronics) before turning on the car ignition and driving the car

When the car is on, the car alternator generates electricity and charges the car battery after the battery has a voltage drop.

But if the car is not on, and you are using the car’s electronics, you are just relying on the car battery to power those electronics.

This is detrimental to the car battery because car batteries are not meant for this type of use.

Instead, car batteries are meant to provide a sudden burst of power for ignition. They’re not made to provide prolonged power for electronics and other devices (that’s what a deep cycle lead acid battery would be for).

Using your car battery as a battery that powers electronics, instead of a battery that just gives you a burst of power for ignition, will damage the battery and greatly shorten it’s lifespan if it’s repeatedly used in this fashion.

So avoid operating any car accessories or electronics while the car is off.


Tip 3: Make sure the car battery is secure and has good battery cables

The battery has to be secured at all times. If a battery is jostling around it will be impaired and could short circuit.

This will ruin the battery – and even cause damage to your car while creating a safety risk.

The same could happen if you have bad battery cables (or they’re not connected properly). So check your cables and make sure they have a secure connection as well.


Tip 4: Insulate your car battery from extreme changes in temperature

Protecting your car battery from large changes in temperature will help maximize the battery’s lifespan.

To do this you can use a car battery insulation kit.

Newer model cars already have these kits installed typically. But if your car doesn’t have one, you can easily install one yourself.

Just make sure it fits your car’s battery compartment. Generally the companies selling these battery insulation kits will have a form on their website where you can put in your car model and year, and it will tell you if your battery will fit their kit.

These protective battery sleeves are usually made of plastic or an acid resistant, thermal resistant material.

These car battery insulation kits will insulate your battery and protect it while still allowing proper ventilation.


Tip 5: Fully charge your car battery at least once a week (use a car battery charger or interchange batteries if you have to)

Your car battery drains even when the car is off.

This happens because current is drawn from the battery by car accessories (radio, lights, etc.) or the car computers.

This is why people come home from long vacations and find their car battery dead.

But to prevent this, you can use either a car battery charger or a solar battery charger.

Car battery chargers (regular or solar) will maintain the optimum charge level of your car battery when the car is not in use.

They do this by providing enough power for the the car accessories and car computer, so they don’t continuously draw current from the car battery when the car is off.

As you can imagine, these chargers are very useful …especially if you go on a trip or leave your car unused for a while.

They’re also useful if you go on a lot of short car trips (like to work and back each day) and never give your battery a chance to fully recharge. Repeatedly doing this will dramatically shorten your battery’s life – unless you use a car battery charger or interchange batteries, leaving one at home to fully charge.

The most important thing to remember with this tip is …make sure you fully charge your car battery at least once a week because it will greatly increase the life of your battery. Do this with a charger, interchanging batteries …or just going on a car ride long enough to recharge the battery.


Tip 6: Check your car battery’s water level

Most car batteries indicate if there is a need for water.

So check the car battery water level indicator regularly and if water is needed, refill the battery with distilled water (and that’s important, ONLY use distilled water to refill your car battery).







Tip 7: Do NOT overcharge your car battery

Never overcharge your car battery. Lead-acid batteries release oxygen and hydrogen gases when they’re overcharged.

This causes two problems:

1. It can be explosive.
2. It also breaks down the composition of the water in the battery – which shortens its lifespan.


Tip 8: Check your car’s alternator

If you’re doing everything we’ve recommended in this article but your car batteries are still dying early, you’ll want to check your car’s alternator (or get a mechanic to check it).

If your alternator is bad it will results in ineffective recharging of your battery and dramatically shorten your battery’s lifespan.




Important Safety Precautions:

Safety Precaution #1) Before disconnecting your car battery read the car owner’s manual first. Most commonly (if not stated otherwise in the owner’s manual) the negative cable is to be disconnected first and then the positive cable. When you re-connect the battery, connect the positive cable first and then the negative cable.

If done in the wrong order it may affect your car’s fuses and other electronics. Also, remove your car keys from the ignition before working on the battery. Some cars are more sensitive to this procedure than others - like German Luxury Cars (Mercedes Benz and BMW type cars) - so use extra caution.

Safety Precaution #2) If you are charging a battery do it in a well ventilated area. If you are handling a car battery that is installed you should open the hood of the car for a few minutes to allow for ventilation first.


What can you do if your battery dies?…

If your car batteries dies or is in the decline phase all hope is not lost! You can still recondition the battery and bring it back to life again.

There’s actually a simple method that you can learn in the EZ Battery Reconditioning program that will bring a dead (or dying) 12v lead acid car battery back to life again.

It’s simple and quick…

And this easy 12v car battery reconditioning method will extend the life of your car battery even longer than the tips we discussed in this article…

…PLUS it will save you money because you can re-use your reconditioned car battery instead of buying a new overpriced battery.

You can learn more here.



dead car battery repair

4/08/2017

7 Ways To Prolong The Life Of Deep Cycle Lead-Acid Batteries


If you use an off-grid alternative energy system, you will need a battery bank with deep cycle batteries.

The most common deep cycle batteries used in off-grid energy systems are (deep cycle) lead-acid batteries because they’re reliable, affordable, and able to repeatedly deeply discharge and recharge.

But a lot is asked of deep cycle lead-acid batteries in off-grid energy systems. The regular deep discharging then recharging they have to perform puts a lot of stress on the batteries.

But if you take proper care of the batteries …and also do a few tips and tricks we’ll teach you in this article, you can maximize the lifespan of your deep cycle batteries.

In this article, we’ll not only show you our top 7 ways to prolong the life of your lead-acid deep cycle batteries…

We’ll also point out some of the most common mistakes we see people making when they use lead-acid deep cycle batteries in their off-grid energy system (so you don’t make the same mistakes)!


The Battery Bank Is The Achilles Heel Of Solar/Wind/Off-Grid Energy Systems

Before we give you our top 7 tips and tricks, we want you to know why this information is important…

- One the most expensive parts of an off-grid energy system is the battery bank.
- And the batteries are typically one of the first things to fail in a system.

Improper battery care often kills the batteries in the battery bank well before their time. This forces people to buy new expensive batteries and also cripples their off-grid system until they replace the dead batteries.

So proper care is critically important so you prevent premature aging of your batteries and maximize their lifespan.




Quick Tip: If your deep cycle lead-acid batteries do die ...or if you just want to save money on your battery bank, you can:

- Get old batteries for free (or dirt cheap if you know where to look)

- Recondition them back to 100% of their original working condition

- And build your battery bank with those batteries instead of new pricey batteries



7 Ways To Extend The Life Of Lead-Acid Deep Cycle Batteries

#1) Use High Quality Batteries

So this tip probably seems obvious, but the old adage ‘You get what you pay for’ holds true for most deep cycle batteries.

Cheap off-brand batteries from China are flooding the market right now and you want to avoid using these. They generally have a much shorter lifespan compared to quality batteries that you pay a little more for upfront.

High quality flat plate batteries can last between 10-12 years. The more expensive tubular plate batteries can even last as long as 20-25 years if maintained properly.

Paying for higher quality batteries upfront that last 10-25 years may seem expensive but it actually ends up being more expensive to buy cheap batteries …then replacing them every couple years (because they die early).

If you want to save money on your battery bank don’t buy “cheap” batteries, instead get quality used batteries and recondition them back to their original condition.


Don't know what batteries to use? If you don't know what kind of batteries to get for your off-grid energy system, read our article about the 3 best batteries for off-grid energy systems.


#2) Proactively Prevent Corrosion

Even if you use the most expensive, high-quality batteries in your battery bank, it won’t be of much use if the batteries aren’t cared for and corrosion or acid is on them.

Before you assemble all of the components of your battery bank, make sure to individually coat the terminals, wire lugs, nuts and bolts with a non-hardening sealant.

You can also apply a thin coating of petroleum jelly to the battery terminals for some extra protection.

Lastly, seal exposed wire at a terminal lug using submersible rubber splice tape or something similar.

The reason all of this has to be done before assembly is because it ensures that all of the parts are equally protected. If you apply protective substances after you finish assembling the system, there is a good chance that dirt will get into small spaces that weren’t properly coated.


#3) Make Sure That the Battery Bank and PV Array are Correctly Sized

If you’re using a solar panel or wind power system, you should make sure that your battery bank is big enough to carry six to ten days of load.

This ensures:

1. You’ll always have a nice back-up supply of power.

2. And you’ll also be able to use your batteries a little more gently so you don’t have to consistently drain them.


#4) Fully Charge The Batteries Every Three Weeks

At the very least, make sure to fully charge your batteries every 3 weeks.

This reduces corrosion on the inside and ensures equalization.




#5) Keep Your Batteries at an Ideal Temperature

Because temperature extremes cause batteries to deteriorate much faster, it is important that you keep your batteries in a place where the temperature is relatively stable.

Aside from enclosed above-ground structures, you can also create a structure that is partially underground. This way the temperature in the structure will remain the same no matter what the weather is like outside.

In addition, make sure that the charge controller or inverter system has a built in temperature compensation feature. This is necessary because the charge voltage limit of a battery increases as temperature drops and decreases at temperatures increase.


#6) Don’t Install More Than Three Parallel Battery Strings

Ideally, your battery bank should only be made up of a single series of cells. The more cells that are included, the higher the chance of there being random defects. There’s also a greater chance of losing equalization, resulting in cells failing prematurely.

If you can’t stick to just a single series of cells in your battery bank, limit it to three parallel battery strings.


#7) Install a Renewable Energy System Digital Monitor

A renewable energy system monitor will help you keep track of the performance of your system (including the battery bank).

It will also help you troubleshoot any issue that comes up with your system so you can troubleshoot it before it turns into a bigger problem.

This will be particularly important if you are relying on the power from your off-grid power system and living in a remote area.

It will also help you maintain your batteries so you don’t have any surprise repairs that are costly and could have been avoided.


What else can you do to make your lead-acid deep cycle batteries last longer?

There are additional ways you can extend the life of your deep cycle lead-acid batteries. We cover all of these methods in the EZ Battery Reconditioning Program.


Additionally, you can also bring old or dead lead-acid deep cycle batteries back to life again with the EZ Battery Reconditioning program.

This will allow you to give your old batteries a “2nd life” so you don’t have to buy new pricey batteries for your battery bank.

Or you can even build an entire battery bank with used batteries that can get for free (or dirt cheap), that you recondition with our system.

You can learn more here.



recondition deep cycle lead acid batteries

4/06/2017

Prolong The Life Of Lithium-ion, Laptop, and Cell Phone Batteries


Some of the most expensive batteries to replace are cell phone and laptop batteries – also known as Lithium-Ion (Li-ion) batteries.

A lot of people don’t realize that poor care and poor charging practices dramatically decrease the battery life of their lithium-ion batteries.

And the most crucial time in Lithium-ion battery care is during early use or when you first get the battery, phone, or laptop.

So to help you prolong and maximize the lifespan of your laptop, cell phone, or other electronic that uses a li-ion batteries (like an electric shaver)…

I’ll teach you what causes a lithium-ion battery to age prematurely …PLUS, tips, tricks, and crucial maintenance information you must know to get the most out of your Li-ion batteries.


So… How Does A Lithium-Ion Battery Work?

Lithium-ion batteries work based on ion movement between negative and positive electrodes.

Theoretically, lithium-ion batteries should work forever. However, high temperatures and cycling decreases their lifespan over time.


How To Prolong The Life of Lithium-Ion Batteries

Follow these tips to prolong the life of your lithium-ion batteries:

- For brand new batteries, it is important to charge them completely before you use the cell phone, laptop, or other electronic. This “teaches” the battery the extent of the charge.

- To prolong the life of a lithium-ion battery that sees a lot of use, like a laptop or cell phone, it’s better to charge it often for short periods of time (one to two hours) instead of charging it from a near dead state each time.

- While short charges are best, it is important to let the battery drain completely and then fully charge around once a month. This help maintain good battery health.

- It’s very detrimental to a lithium-ion battery if you use the device while it’s charging. This makes the battery overheat, which lowers a li-ion battery’s lifespan.

- If possible, use a charger with a lower voltage rating. While this will charge more slowly, it will charge at a lower temperature, preserving the battery.

- Never leave the battery in sunny or hot areas. This heat can damage the battery life.

- Finally, if you aren’t going to use the battery for a while or you’re storing it, make sure the battery is over 40% charged before you put it away. When lithium-ion batteries are stored out of charge for long periods of time, this can lead to an inability to maintain a charge once the battery is in use again.

If you follow these tips (especially if you use them from when you first get your new battery, phone, laptop, or other electronic using a lithium-ion (Li-ion) battery) you will maximize the battery’s lifespan and prevent premature aging in the battery.


What Can You Do If A Battery Does Die Or It’s Performance is Suffering?…

If a battery is aging or dies early on you, you can bring those old batteries back to 100% of their working condition using the EZ Battery Reconditioning program.

In this program, you’ll learn how to bring old cell phone, laptop, car, deep-cycle, golf-cart, marine, and forklift batteries back to life again (plus many other types of batteries too)!

The battery reconditioning methods are easy to do and they will save you a lot of money on battery costs over your lifetime.

You can learn more by clicking here.



repair mobile phone battery