NiMH batteries produce 1.2v each. When you see a 4.8v listing it's because they've stacked 4 small cells together. Li-ion batteries are 4.2v each. The advantage Li-ion batteries have is the amount of energy they can store in a small package. A stack of 4 NiMH batteries have a storage capacity of around 600 mah in a package the size of an 18650 battery. AW recently came out with an 18650 protected Li-ion battery rated at 3100 mah. The discharge rate is also higher with Li-ion cells, which allows it to release energy quicker. Some people feel that NiMH batteries are the way to go because they are a safer chemistry, and they are safer. But Li-ion chemistry is quite safe if you take simple precautions. ECF now has a battery safety page that everyone who uses PV's should read.
There is only one vv mod that I know of which might take a pair of 4.8v NiMH's. You'd have to ask the manufacturer if the
Big Daddy Meter Mod would work with those batteries.
