It all started when my Kill A Watt stopped working. This is the device that measures my power consumption when I am charging. I also use it to verify that all of my chargers are working by the amount of power being consumed when I first plug it in. Generally, this is 1020-1070W after a commute. So I have been going without it for the last week. I have a good idea of when it is charged anyway, so I figured it wouldn't hurt to go without it until a replacement arrives.
Last night on my way home from work at midnight I started going up the one kilometer long hill when I noticed that the system voltage was lower than normal - 65V instead of the normal 68V at full throttle. So I reached over, grabbed my battery monitors and plugged them it. I gasped at what I saw: five pairs of batteries at a normal 11.5V and one pair at 5.5V! For those who don't know, anything under 10.5V for any amount of time is battery murder territory.
I feather footed it the rest of the way home, keeping the weak pair above 6V. At home I tinkered around for a bit and soon realized that one of my chargers was not charging. It turned out to be a fuse, which I replaced and it worked again.
The scary part was that I had been noticing the car was a little bit weaker the last few days, but I just attributed it to the colder weather. I really have no idea how long the one charger wasn't working and I had a bad feeling that I had murdered one pair of batteries.
I charged the pack over night and today during the day and the heavily discharged pair took 14-1/2 hours to charge. Normal is three hours if I fully charge after a drive home from work. I then split this pair and let them sit all day so I could check resting voltage to detect any internal shorts or weird self-discharging. They both rest at 13.84-13.88V, so it appears that they may live after all.
I will definitely be more careful to make sure all chargers are turning on from now on, at least until the new Kill A Watt arrives.