Google rexs speed shop - they have 12v conversion kits for 70 quid for an xt 250. I have emailed hime twice with quires but have had no reply.
I had my tt upgraded to a 22 litre tank in 1993 at tt outrider in st peters which is no longer there. They sold conversion kits for tts including 12 v conversion, oil cooler panniers big tanks the whole deal. Jeeze they would be handy now i have money.
But by chance i spotteda post referring to the owner so i have pm'd him about how they did the 12 v conversion.
They used to sell these kitted up as adventure bikes - good guys. Bumped into the guy who bolted my tank on at a road house in alice springs when i roder her acroos australia in 93'.