At the beginning of the last winter, the 12 volt battery in the HCH II was unfortunately completely drained by a done light that was left on. After charging it up again, the indicator has consistently shown a good battery and there have been no obvious issues with it. I've had a drop in mpg to the low 40s consistently, and the IMA battery is having increased fluctuations, with crashes even in cool weather when half to almost fully charged (no codes yet). Could a dying 12 volt battery be putting a load on the DC-DC and the IMA battery, causing the lower charge state and lower mileage? Or is my IMA battery going at only 41K?