Message #3 Posted by Andrés C. Rodríguez (Argentina) on 11 July 2002, 4:59 p.m.,
in response to message #2 by Ron Meek
Well, voltage and current are usually related (the simpler case is Ohm's Law, where V = I * R); even in a charger there is a relationship, but depending on the design the relation may be not so simple.
Simple chargers apply a current which usually is 10% of the rated capacity of the cell, so a 500 mAh cell receive 50 mA. Usually it takes some 14 hours to charge a fully discharged cell, and about 8 hours to replenish a partially discharged one.
Intelligent chargers allow for shorter charging times, but to avoid overcharging, overheating, venting or even explosion of the cell, they monitor internal resistance, charge level, temperature, or other condition of the charging cell, and adjust the current as a function of such.
As different cell chemistries (NiCd, NiMH) have different behavior about charging times, current profiles, temperature increases during charging, etc; it is advisable to use an external charger for the specific kind of batteries you are working with.