Claims of fast charging a Li-ion battery in one hour or less usually results in lower charge levels. Such a charger simply eliminates stage two and goes directly into 'ready' once the voltage threshold is reached at the end of stage one. The charge level at this point is about 70%. The topping charge typically takes twice as long as the initial charge.
Depending on the charger and the self discharge of the Hitachi WH 8DYA Power Tools battery, a topping charge may be implemented once every 500 hours or 20 days. Typically, the charge kicks in when the open terminal voltage drops to 4.05 volts per cell and turns off when it reaches 4.20V/cell.
No trickle charge is applied because the Li-ion Power Tools battery is unable to absorb overcharge. Trickle charge could cause plating of metallic lithium, a condition that makes the cell unstable. Instead, a brief topping charge is applied to compensate for the small amount of self-discharge the battery and its protective circuit consume.
