|My "refurbished" pack.|
I opened carefully the third pack so that I could reuse at least the lower part of the case, as a container for the 4S2P battery. Working with an open pack allows you to check voltages across single (group of) cells, so they can be characterised and, in case, replaced.
Fed with 18V, "the thing" drew 1.8A for a rather long while (hours). Then it stopped at 4.0V per cell without heating. The pack now measured 16V and the charger electronics reported 100% charge even after the night at rest.
Meanwhile I located the datasheet of these cells, and they seem to be Lithium-Cobalt batteries, a technology rated for 1C discharge current (ref. "battery university" website). I hoped for better, because they might not sustain the FT817 at 5W :-) Also, the datasheet calls for protection circuitry in case cells are paralleled together, while this high brand battery pack did not carry any!
Now I need a DC lamp to discharge the pack and test a full discharge-charge cycle, to get an estimate of the residual mAh capacity.