Lightweight race Battery Box

I've been really tempted to get a lightweight race battery, but although they are over 2kg lighter, they are not physically much smaller.  I'm not all that keen on having a 3kg lump hanging off the subframe, it'll help wreck it in a crash, but i talked myself out of getting the lightweight battery because i'm not sure of the power/weight of the bike.  I don't want to save the 2kg in battery weight only to have to add it back on as lead.... that'd be some very expensive lead.

There's no way the old battery box will fit, so i've been making a new one from some aluminium sheet I had spare.  I'm starting to get the hang of aluminium welding. I lengthened a steel bicycle seat post just before this and my steel welding is still mines better, but i'm getting there.

 Nearly finished battery box, i intend to have a velcro strap hold it in, which explains the raised bit in the middle.

Mounting lugs welded onto the side.  Luckily it just slides/twists into the subframe for mounting... for a little while I started to panic thinking I'd c*cked it up.