Please tell me if the following is correct (or advice me if not) regarding parallel cell configurations in flashlights. The second item under critical is based on my intuition and not on anything specific I have read. It seems a cell that wants to be at a lower voltage would draw from the other cells.
Critical:
Only load flashlight with cells charged to the same voltage.
Only use cells that have the same resting voltage (say 3 weeks after being charged)
Not Critical:
Cells of equal capacity
Cells with same discharge curve
Is the above correct for parallel configuration flashlights? I understand why the “Not Critical” items are critical for serial configurations, but it would seem they are not for parallel. I imagine it is good practice to match capcity and discharge curves, but most of us don’t have the equipment to measure these characteristics.
I read that parallel configurations are safer, but haven’t read anything about the mechanics of why parallel is safer. I’m guessing that it is because the parallel cells contribute their own current, but the total amount of current used by the driver/leds does not flow through each of the batteries.
The only thing that’s really critical is that they have a SIMILAR voltage when they are put into the carrier together. This will prevent HIGH current charging between the cells. Once they’re hooked together, however, the other items become non-critical.
Resting voltage, for instance, isn’t critical because when they are in parallel, they WILL have the same resting voltage - if one has a higher internal self-discharge rate, for instance, the other will give up a little current to keep them equal.
Cells with similar capacity is a good idea - I wouldn’t match a 1600mAh with a 3100mAh, for instance. A 2900mAh and a 3100mAh (or some combination of similar dissimilarity) would be fine though.
Same discharge curve is nice to have, but again, non critical. The stronger cell will give up current at a faster rate to keep the two (three/four/five whatever) cells equal throughout the discharge.
IIRC, HKJ did a test with that, and while there were high currents for a short amount of time they quickly settled to a safe level without the cells ever heating up/venting.