Some chargers feature a variety of adaptable sizes, meaning you can charger AA and AAA on the same terminals. If you’ve got a lot of different-sized batteries, this would be an ideal choice. Rapid-chargers are similar to regular chargers, but often don’t have a charge-control mechanism that halts or slows the flow of voltage. These are effective at quickly charging batteries, but can reduce the life of the battery more significantly. [1] X Research source

Nickel–metal hydride (NiMH) batteries are common in consumer products, especially power tools, while lithium-ion batteries are common in electronics. Both varieties of battery are commonly used and both are rechargeable. When you first start to use a new set of rechargeable batteries, run them completely down before recharging them. This will decrease the possibility of a phenomenon called “memory effect,” which is when the battery’s capacity diminishes from being recharged prematurely. [2] X Research source Use a battery tester to determine if there is life left in a battery before attempting to recharge it. Many battery testers are inexpensive, easy to use and provide an instant reading.

Always defer to the manufacturer’s instructions. Read the battery charger instruction manual thoroughly, which should contain important information, including the time it takes to complete charging, a key to indicator lights and safety information specific to the batteries being used.

On most A/C chargers, there should be a diagram showing you how to orient the batteries properly. Generally, the flat side of the battery should rest against the spring, and the “bump” on the battery should rest against the flatter side.

“Trickle charge” is a technique of lowering the charge to roughly 10 percent of the capacity of the battery, which is usually enough to keep a battery fully charged, without triggering the discharge that results in a diminished capacity of battery life. [3] X Research source Most manufacturer’s don’t recommend long-term trickle charging, but if you have a charger with an adjustable charge rate, dropping it to a lower rate can be an effective way of keeping your batteries juiced.

It is possible to charge a battery without removing it, but you need to know whether or not the battery is grounded to the chassis, to avoid clipping the negative in the wrong place. If it is grounded to the chassis, clip the positive to the positive terminal, and the negative to the chassis. If it isn’t, then clip the negative charger to the negative terminal, and the positive to the chassis. [4] X Research source If you want to know how to jump your vehicle, read this article.

Refill each cell with distilled water, to the proper manufacturer levels, if necessary. Do not overfill. Some lead-acid batteries won’t have removable ports, so defer to the manufacturer’s instructions as always.

Some chargers are manual, which means you’ll have to shut them off when the battery is fully charged, while other automatic batteries will shut off when the battery is full. Other than that, and slight differences in design, all chargers work in essentially the same way. Again, if you’re not sure, head to the auto-parts store for a quick check. You don’t have to pay for it, and you’ll be sure you’ve got the right info.

First, connect the positive cable, which is usually the ungrounded one. Next, connect a jumper cable or an insulated battery cable that’s at least two feet long to the negative post, and connect the negative battery cable to this cable. If the battery is still in the car, you’ll want to clip the ungrounded cable to the ungrounded peg on the battery, and the grounded cable somewhere to the chassis of the car. Never clip a charger to the carburetor, fuel lines, or the body of the vehicle.

If you want to know how to use a voltmeter to do this, read this article.