Before changing ATV batteries, you need to make sure the alternator is charging properly. Hook a battery charger to the battery. Allow the battery to charge. Start the ATV, then test the alternator with a voltmeter. If the alternator is charging properly, it will show from 13 to 14 volts across the battery terminal while the ATV is running. Any readings below this level mean that the alternator is failing and must be replaced. If you don't replace it, you'll just drain a new battery.
Finding Replacement Batteries
If an ATV battery refuses to hold a charge, or will not take a charge, you will need to replace it. Before purchasing a new battery, check the label. The replacement battery must have the same specifications for amps and voltage. Most auto parts dealers that carry batteries for ATVs also have the ability to look up the battery via the year, make and model of the ATV. If you get something that's too powerful, you'll overload the electrical components and be stuck with a big repair bill that ATV insurance won't cover.
Most ATV batteries are located under the seat. No matter where the battery is located, the process to change it is the same once you gain access to it.
Remove the negative battery cable. Lay it to the side, making sure it does not touch anything made of metal. The negative cable will have a black wire connected to it. There is usually a minus sign on the battery terminal, denoting that it's a ground.
Remove the positive battery cable and lay it to the side. The positive battery cable generally has a red wire attached to it, and you'll see a plus sign on the battery post. If there is a battery hold-down bar, remove it with a socket or wrench. Lift the battery out of its casing.
Set the new battery into the casing. Replace the battery hold-down bar, then attach the positive battery cable. Tighten the cable snugly, but do not over tighten it, as you could break the retainer. Attach the negative cable in the same manner. Make sure the black cable goes to the negative battery post and the red cable goes to the positive battery post.
To keep the battery from getting a build up of green battery acid on the terminals, glue a penny 1/16 of an inch away from each battery post. Superglue is the best material for this. Make sure the pennies do not touch the battery posts or the terminals, as that will short out the battery. The pennies will attract any battery acid that leaks, keeping it from corroding the battery cables.
If recreational riding appeals to you, an electric ATV may have some strong advantages over a gas-powered model, even though you'll be sacrificing some speed and power.