HP41, N battery (N Cell), charging of HR1

[Dave Frederickson]

Smart chargers primarily detect end-of-charge using -deltaV. That is the charging voltage will drop a little when the battery is full. For the -deltaV circuitry to properly detect end-of-charge the charge current should be 0.3 to 0.5C where C is the capacity of the battery. If you charge too slowly then end-of-charge is detected by temperature.

So you're in the market for a new smart charger. The favorite BC-700 has been discontinued in favor of the BC-1000 with higher current capability. Another favorite, the Wizard One has also been discontinued and replaced by the MH-C9000PRO which sports exactly the same specs but only has 4 modes of operation compared to the Wizard One's 5.

I haven't found a good source for N-cell NiMH (HR1) batteries. EBL had some 600 mAH cells but they're no longer being sold in the US.

Finally, that was a spectacular explosion!