Putting in 2 extra batteries?

[NeedMorePower]

Thanks for the thoughts and tips guys. My current ground location seems decent with just one battery in the back while cruising and hammering. However, when I come to a slow roll or sitting, my voltage will drop a bit on heavier slams, down to about 12.8-12.5 on average. When the music is turned down or if bass is moderate, the drop while sitting is minimal. While cruising I average 14.0 to 13.5 on cool days, this is with slamming the sub. This is about 13.8 to 13.3 on warmer days. And it is with a unibody car. I may do a run to the front to see how well it stabilizes.