I also did the battery forward mod and I finally got rid of the understeering. It made a huge difference but now the rear end is very very loose and has way too much oversteering. It got way harder to control and has less traction when accelerating. So far I pretty much ran the softest spring set up, really low roll center,... on astro turf.
Should I use harder springs in the front and/or raise the roll center? Would that be any help?