Datasheet

You may also run across 4.1V/3.6V batteries. These are older than 4.2V/3.7V - they use a slightly different chemistry

and you'll see the 3.6V marking on the cell.

Nowadays you may also be able to purchase 4.35V cells! These are the latest chemistry, they have a little more power

as indicated by the voltage being higher than 4.2V. They tend to be cylinder lithium ion's used for laptop batteries, and

lights so its not terribly likely you'll just run into one unless you're looking for it.

Make sure when you're buying batteries and chargers to match them up! Overcharging a 3.6V battery by attaching it

to a 4.2V battery charger can at the very least permanently damage your battery and at worst cause a fire!