The battery charger…
is more complex that the battery. Sensing 5-10 millivolts for nickel-metal, and peak voltage for SLA and li-ion – the battery charger electronics cannot be taken for granted if you want safe and reliable run time for your host.
Nickel battery chargers..
Sense voltage deflections of 10 millionths of a volt per cell to determine charge completion.
Nickel cadmium batteries/chargers are disappearing for environmental (cadmium is a heavy metal) and memory effect reasons.
Nickel metal hydride (NiMH) batteries are without heavy metal and are easier to clear when memory set in – with 1-2 discharge/charges.
Li-ion battery chargers ..
Regulate the constant voltage to 30-40 millionths of a volt to maintain a full and safe charge.
You loose 5-10% of the li-ion battery capacity when you lower this voltage to insure safety but gain battery cycles in return.
Li-ion batteries are without memory. If you charge the battery frequently you actually extend the battery cycle life.