18650 host "swap-out" protection cuircuit

I don't know if anyone has tried this before but here is an idea I have been playing with: modifying a single or double 18650 host so that you can insert a 18650 protection circuit behind a unprotected 18650 effectively allowing you to temporarily turn any unprotected cell into a protected one while it is in use. What I am thinking of doing is cutting a narrow channel down the inside wall of the battery tube to allow for a metal disk (insulated around the edges) with a wire attached for the positive terminal of the battery.

Another idea is having the same set up...but somehow building it into the tail-cap of the flashlight...this would mean you would have to overcome the problem of connecting the protection circuit with the positive terminal of the battery without shorting it...but this should be overcame without too much fuss.

Positives I can think of: Unprotected cells are cheaper. Can use any unprotected 18650 cell and effectivily make it protected.

Negatives: Unprotected cells are still just that when out of the host (e.g charging). Could get fiddly when swapping cells (hence the idea about building it into the tail cap) May not work with cells with protection circuits (due to space constraints)

So here are my questions: Will it work with pre protected cells (if space allows)? I see no reason why it wouldn't but I am no expert.

In your opinion..do the negatives outweigh the positives?


I think not. Also for nagatives, when the protection pcb fails all of your your batteries overdischarge instead of the faulty one.

If I understand correctly...you are talking about having the PCB in the tail...covering both cells (in which case you are right...which means this option is only viable for single 18650 hosts). The stumbling block with the cell shorting out when the tail cap is screwed on (for tail-cap method) is perhaps larger then I thought...which basically limits me to the manual placement method (unless they were built into a 18650 holder of some sort..again the limiting factor here is space).