Ross - I guess we'll find out soon enough. I was originally convinced I had a bad pack, and that's why I bought a good used one just like you did. After reading this first post from Robert Smalls, I changed my tune. I will find out soon enough.
My understanding is that there are two possible issues 1) Cell imbalance, or 2) True degradation of capacity. Using these batteries from 20 to 80% was supposed to make them last 30+ years (unless they were abused). The degradation issue supposedly causes an IMA light. The cell imbalance just causes tons of re-cals which takes out 10MPG's of mileage with all the re-gens, hidden regens, and re-cals - not to mention the loss of power (since it won't allow assist when re-cal).
I can't find anything on the web about why one NIMH battery pack would discharge faster than another with no load connected. I have a theory but I'll save it until I can prove this out.
The large spike of current/voltage you read about could be for the 'cell reversal' issue. If NIMH batteries/pack sit too long, one or some cells will reverse and become a Load that dissipates the others. A large voltage spike will take the cell out of reversal so it can be charged with a normal charger.
I don't believe my pack has any reversed cells or it would have gone up in smoke by now with the high voltage I brought it up to!