I was given a faulty battery charger that was DOA when bought, except they never bothered checking it, and now it is too late to return. The charger is an "Ultra Rapid Charger":
I did find a cold solder joint inside that I fixed. I tested the charger with four AA size Ni-Cd batteries, but after about two hours I disconnected as it was getting so hot. The batteries were also quite hot, a lot warmer that with other chargers. Two of the batteries were flat before charging while the other had some juice left in them, though not sure how much. The batteries now seem to be fully charged. I am reluctant to declare the charger repaired, I am concerned about safety.
Any comment on the above?