A viewer sent in a Milwaukee 12V battery that went weak after a few uses, slow speed and wrong sound in the tool; opened up, it’s not Milwaukee OEM but a cheap pack someone else built. Multimeter reads a bit over 12V total, normal; swap for domestic 2500mAh cells (the ones he uses himself); the Zoyi multimeter reads the new cells at 12.42/12.48/12.46mΩ, the old cells that came out at 55/56/57mΩ — IR that high is never going to work well in a power tool. Fish paper on the new cells’ positives for insulation. The AWithZ handheld spot welder is handier for the welding; 0.1 nickel strip, no effort at all; he had thought of building a big welder but doesn’t use one much so gave up, a small one is enough for occasional use; 0.1 welded on, you can’t pull it off by hand. The main negative reuses the 0.15 strip taken off earlier, and it needs max gear to hold; this machine welds at most 0.15, 0.2 won’t hold. Pack reads 10.7V, IR 46.9mΩ. Reassembled and charged a while, then tested: better sound, high speed fine too, not fully charged so not at its best yet but much better than before. Comments: just pick three JP30s and drop them in (that works); is a drill’s weakness related to the battery; multimeter recommendation / are you using it as an IR meter.