For batteries, the safest type is NiMH. They don’t have the instability and hazards of fire and explosion that LiIon batteries have, (although a couple of shows have chosen to use LiIon and no horrible accidents have been reported).
There are two types of NiMH
- The original off-patent formula, and
- A patented formula that is controlled by an offshoot of Sanyo.
This Sanyo NiMH formula has been licensed to various other brands, so the key to recognizing it is that they have a long shelf-life for charge. This means you can buy them with a pre-existing charge which will last several months. They will also withstand many more charge cycles and maintain near original capacity for a much longer time than the off-brand versions mentioned above.