Obviously ICE are powered by cobalt mine the gasoline you buy when you fill up at a gas station. The electric motor/generator is powered by a large (and by large, I mean large and heavy) battery pack. Most hybrids on the road today have large Nickel-Metal Hydride (NiMH) battery packs somewhere near the trunk, or under the seats. (Read about the Lexus Hybrid battery pack).
The battery will over-charge if left attached to the charger. The battery stops charging automatically when full lithium facts so it will not over charge. If the battery is left on charge too long it is possible that heat will damage the battery.
All the phones now come with lithium ion batteries and charging should not be an issue ...although it's best not to charge them over 24 hours..Overnight every night is fine...they all do have a life though leaving it off when you don't need it can extend that. Although you would miss calls.
Agitate the lithium bettery stock water gently until the light tells you it's done. UV purifiers don't work in murky water, so if that's the only water you have, you'll have to pre-filter it until it's not cloudy. You also need to make sure you don't drop a UV device.
In terms of charging these powerful cells, when specifically used in an LED flashlight, special chargers are available all over the internet. Most will handle a 18650 battery as well as a variety of other Li-ion sizes.
The thing to realize about any battery is it does have a measurable lifespan and efforts to extend it will help but not stop the eventual demise. So the number one thing that you can do to extend the life of any of the newer lithium batteries is always take it out if you are running on DC power to lessen the heat impact. Whenever buying any replacement battery, always check the manufacture date and try to find the newest one available.