Haven't heard of anything less expensive to charge the main batteries with other than the internal combustion engine. Leaving home with a full charge and not using the ICE for recharge you would probably be leaving the car at work with a depleted battery a lot, even if was only a few miles.
I would suggest that you just endeavor to keep your tank full at all times when there is no strike. 12 gallon tank and only a couple of miles of use should keep you out of trouble.
I would suggest that you just endeavor to keep your tank full at all times when there is no strike. 12 gallon tank and only a couple of miles of use should keep you out of trouble.