Join Date: Mar 2015
Location: Pittsburgh, USA
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I ran my 12V battery down once due to leaving lights on, recharged it, and everything was fine. I'm sure that for many other people, this has happened too. You can remove and replace the 12V battery and nothing bad will happen.
We are working on various hypotheses for recent reports of HV battery packs being bricked after several months of storage. The common denominator was that the 12V battery was also dead - or in one case it was deliberately removed from the car to be kept indoors for winter storage. The hypothesis is that a dead 12V battery might be bricking the HV pack, but, even then, only if the 12V battery sits dead for a long time period - months. But it might be something else that is causing the problem.
Somebody at MB knows what the problem is, but they are not talking.
So, out of an abundance of caution, If you are storing your car for more than 3 weeks, I would recommend connecting a maintenance charger (trickle charger) to the 12V battery.
But unrelated to this, in warm temperatures, you should also NOT store the car plugged in for charging. It should be stored in a shady place with an indicated SOC of 60-80 percent or so for minimizing any time-related capacity degradation of the pack. You should keep the pack at a less than full state and in the shade as much as possible during regular use too - especially in hot weather.
So in your case where you are using it only a couple times a week, keep it about 60 percent, and do only partial charges whenever you don't need the full range. But, every 10 charges or so, you should charge it full, as charging full is needed to be sure all cells stay balanced (i.e. charged to same voltage).