Why are different currents used for charging batteries with the same voltage output?

Question

I'm trying to understand the behavior of batteries a bit more. I've noticed that chargers for given batteries have different current capabilities. Do batteries need to be charged with a voltage that is near their nominal output? E.g., a 12V battery should be charged with 12V? If one charger for a battery has a 1A output and the other has a 2A output, is the higher current charger actually just supplying a higher voltage?

The batteries don't have some kind of semi-conductor-like physics going on which allows them to maintain a constant voltage drop with different current levels, do they?

Answer 1

Batteries are usually charged with a bit more voltage than their "full" voltage, but the details vary widely. Often batteries that are deeply discharged need to be brought up slowly until they are reasonably full. Most batteries can be charged with simple logic that applies some fixed voltage or some fixed current, whichever is lower, if you're willing to give up some charging time. Even that doesn't apply universally though, like with NiMH. If you want the fastest possible charging time, you have to carefully do what the datasheet says to do.

A 2 A charger isn't going to produce a higher voltage than a 1 A charger, but it has more current capability. That means it is intended to charge a larger battery, all else being equal.

For the best answer, read the datasheet for the particular battery you want to charge and don't assume it applies to any other battery.

Answer 2

A battery charger must produce a voltage a little higher than the battery voltage - how much higher depends on the battery chemistry, temperature, and other things.

1 Amp and 2 Amp chargers for a given battery type will produce the same final voltage, but the 2 Amp charger can deliver a higher currrent into a discharged battery. With both chargers, the actual charging current will decrease as the battery approaches full charge.