[mcguyver]

Likely you've reversed cell polarity. This can occur from charging in reverse polarity. Perhaps the batteries were manufactured with the (+) and (-) wires incorrectly attached. This often happens with packs built by thumbless monkeys at battery shops.

Not all batteries blow up when charged revers polarity. Many will take the partial charge, but with no current capacity.

Recheck your pack, cut the heatshrink off it if necessary. The indented end (if apllicable) or with the central contact is the positive. Follow the path from positive to negative throughout the pack to see if their wiring is correct.