interesting idea, please help. i'm somewhat a noob

7Ahx12V=84Wh your draw is 19.4Wh, that gives you in a perfect world (it isn't) 4.43 hours of run time. Make sure you're using deep discharge SLAs.

Google battery discharge curve to see how SLA compares to NiCAD, NiMH & LiON. PS they all use different charging methods.