battery charging

Cant mess with van wiring, new tablet battery: $800 bucks as battery is not serviceable. The gel battery is between lighter and tablet powerlug (12v to 5v 1500ma charger via usb port) , inverter is out as it would involve van wire harness mod. My solution cost me 5 bucks...working so far, everything shuts down after 10 minutes anyway so nothing is hot after hours. i left enough wire to store battery behind bulkhead. Well see, it was so bad that when i started my van, the power gets cut to socket for a split second and my tablet would die, with a 2 minute reboot. Motorolla Xyboard, $800 piece of crap...