like i said the best thing to do is just buy a 12 volt pure sine wave inverter to start with. by the time you apply a presidential solution of parallel switch and extra battery and lost room the new inverter is cheaper. if you need a pix send me your email and i will send one.

 

If your running any thing for much time [ with out the engine running ] , then a separate battery is very important and will save you money & grief , not be able to start the engine after drawing down the starting battery , and shortening the life of then also .