Lead acid batteries do not like to be drained all the way, and in fact may not recharge if totally discharged. Lead acid batteries don't like to be discharged more than 50% of their rated amp hours on a regular basis. I don't know why Ford would use a cheap lead acid 12v battery when there are many Li-ion and LiFePO4 batteries that have built in battery management circuits that turns the battery OFF when it gets to low, so it doesn't fail. These batteries also allow about 80% of the rated amp hours to be used on a regular basis like the MME main battery pack. Wonder if the 12v lead acid battery can be replaced with a LiFePO4 battery. The charger specs would be needed.