I noticed that my battery pack was giving me intermittent results, so I removed the heatshrink outer and found this:
The leads have had their insulation stripped too far back. As a result when the leads can short out! This is not good.
Anyway, here's the fix process:
- remove outer heatshrink;
- peel back insulation from top of pack;
- unsolder 'balance' wire that runs from PCB at bottom of pack to battery terminals on top of pack;
- tilt back PCB to get access to lead pads;
- unsolder leads, cut shorter, re-tin and solder back on.
Reassembly is reverse of above procedure.
If you don't have any large enough heatshrink, then wrap pack back up with electrical tape.
I've now got some heatshrink in a size that just covers the 4 x 18650 packs. Works really well: