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Originally Posted by claretant
Does anyone know if the charging process can work in reverse? I mean, if you have a battery pack with ni-mh recharegeables that carry less charge than the internal iriver battery, will the latter discharge into the former? Is this possible, or am I just power-paranoid?
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Not knowing the recharge circuit, let's try and apply what we do know about the batteries.
Recharging of the internal battery causes the cell voltage to increase. As the voltage builds, the current draw from the battery pack will decrease. At the same time the voltage on the battery pack will drop as well.
However the battery pack voltage is starting up around 4.8V while the iHP battery is starting around 2.7-3V.
NiMH don't have a low voltage cutoff like Li-ion-poly cells. So as long as there is a current flow from the battery pack, it should be recharging the internal cell.
The question is whether or not the max 3.6V of the lithium cell is sufficient to start a reverse charging of 4.8V worth of NiMH or even if they show up as a discharge load...
I think not, even if a reverse current flow were possible, I think the lower voltage of the Li cell is too low to do much charging in the NiMH. I think you need much higher voltages, like 5V or higher.
But this is a guess. One way to find out would be to hook up discharged battery pack (measure voltage first) and hook it up to charge circuit of iHP for 30 minutes or so and then remeasure the battery pack voltage. If it increased, then discharging of the internal battery is indeed possible.
If that happens, a diode on the (+) line should stop reverse charging.