I think most people that use this forum would say - you can't beat fitting new batteries! Having said that I saw this feature in the FLT news letter a few weeks back, the theory looks good, check out the link:
www dot forkliftaction dot com/news/newsdisplay dot aspx?nwid=6136

I sent the link to some of my colleagues to see what they thought..........nobody answered! perhaps that says it all!