NiMH are about 1.3V during operation (a little higher than the NiCd they replaced, but drop
noticeably during discharge). NiZn are 1.7V or so and need different charger (or a modern smart
charger that can automatically figure it out).
NiCd 1.2
NiMH 1.3
zinc-carbon 1.5
alkaline 1.5
NiZn 1.7
Pb/PbO2 2.0
non-rechargable lithium 3.0
LiFePO4 3.2
other Li-ion and LiPo 3.7
New rechargables are usually sold without much charge, so the first thing you do is charge them.