Once the battery had been rinsed out copiously, I used a sharp tenon saw for the lobotomy, along a suitable seam, and completed removing the guts with a Fein Super-Cut (without which, frankly, I wouldn't have tried it). The Fein enables you to neatly chop out all the baffling and section the lead-work with a minimum of contortion.
I wore eye-protection, gloves, did it outside in a well-ventilated courtyard, washed everything thoroughly, disposed of the contents responsibly, no animals were harmed during the experience, so spare me any health-and-safety preaching. My car's got no air-bags, head-rests, or ABS, and if I roll it I'm dead.
This battery is a perfect fit inside the case, needs a couple of judiciously-placed rubber blocks etc - but if you can hack this kind of modification you can work out the details for yourself.
http://www.motobikestore.com/scheda.asp ... 19&ID=4711
The roof isn?t particularly stable once the cells have gone, and nor are the terminal posts, so I screwed it to a board to keep it flat, and laid 2-3 layers of fibre-glass cloth plus resin stuffed into all the available crevices, whilst incorporating an angled strip at each end to give me a positive location of the lid on the case, see pictures. Then I painted it black because it looks fairly horrible. The terminal posts were drilled/tapped 1/4 UNF and stainless studding loctited into place.
25mm² wires and crimped fittings fit comfortably on either side of the battery inside the new case, and the original top frame and tie-downs go back as before.
The only failing is that the top warps slightly (see the uneven gap when viewed from the side) because I've used the lid to constrain the new battery vertically ; one day I'll make a strap to clamp the new one, and the old case will become purely cosmetic.
The only potential weakness, that I can see, of this solution, is the 26 Ah autonomy, half the original, but the doubled 900A cranking power starts the car like it never has before and I never leave the car parked with its lights on anyway.
