6 cell question
 

if i do 6 cell.....can i use 4 batts that have 700mah and 2 that have 550 mah? will that hurt the car?

It's usually not a good idea to mix battery types. What will happen is when the smaller ones drain, the larger ones try to charge them and it causes weird things to happen with reverse currents, etc.

If possible, always try to match battery types.

i would think so...but then again im not a complete know it all on electronics, but mixing batteries isn't a good idea man.