can i charge a 7.2V 1080mAH battery to 8.4V 0.9A charger?*Theory explanation pls.
I presume you mean, can i charge a 7.2V 1080mAH battery *with an* 8.4V 0.9A charger?. Yes, but you must be careful. mAH (milliampere-hours) is a unit of charge; in Coulombs, 1mAH 3.6C. An unregulated 8.4V, 900mA charger will generate WV*A 7.56 Watts. 7.56 Watts through a 7.2V drop will try to draw 1.05 Amps; if the charger has current limiting circuitry, this will work fine- the battery will absorb the required 3888C at 7.56W in 9 minutes or so (this is an ideal figure- internal resistance will increase actual charging time considerably). If the charger is not current limited, the charger and/or battery can easily (and quickly) overheat. This can destroy your charger, rupture your battery, and start a fire. If you're charging a Lithium Polymer battery, all bets are off- overcurrent turns LiPo batteries into bombs. Again, be careful if you try this.
