You may have screwed your battery pack by letting it get that low. It's an 8 cell pack and should never be allowed to drop below about 1.1 volts per cell, or 8.8 volts. If cells get below about 0.9 volts per cell there's a good chance that one of them will "reverse", and you get to throw away what was a good pack.

You do not have to discharge your packs before recharging. It's a good idea to cycle them two or three times a year, but by using a cycler. If you're not going to invest in a cycler, just charge them overnight before you go to the field.

I'm guessing it was the extremely low voltage, or a reversed cell that fouled up your transmitter. I'd start by replacing the pack.

Good luck,
Dennis-