The 1512 2d is a amp hungry motor and it probably pulled too many amps when the battery was nearing the LVC. I would set the LVC to 3.2 volts. Zippy batteries are great for the money, but I find they can't withstand dropping below voltage under load as well as the higher cost brands. For this reason, you need to set the LVC to 3.2 to be safe. You can get away with a 3 volt LVC with the enerland based cell packs but not the zippys. Especially with a high amp motor like the 1512 2d.