Thread: Battery backup for drained SLA's

I know the title sound odd but here is my idea; I started my car up from work and realized, "Crap, my battery's dead". I must have left my lights on. However after a buddy gave me a jump i went home and started working on a plan to remedy this problem (I live in a foggy area, and I tend to leave my lights on). My plan is simple, use four of these diodes (http://pdf1.alldatasheet.com/datashe.../datasheet.pdf)
put them in parallel so they can handle the current draw, then I use my silicon mats to mount them to the car chassis to dissipate heat. Next I'll make it so the current can only flow from the primary starter battery. After this I will use an 80 amp relay controlled by a switch in the cabin of my car. I am using an 8AH battery which is sufficient for my SUV (KIA Sportage 01). How this works is it keep my primary battery from draining by not allowing the current to pass through the diodes, unless the car has been started, and after the car has been started a relay is setup to go on and charge my battery off of the alternator. So the next time my battery is dead I flip a switch and start my car up as usual. Also the alt in my car is a 136amp 06 Dakota.
Sound good? Tell me what you think.