I had the opposite problem – I used to have the bag & my new bike frame doesn’t have a long enough space to mount it – I’ve got the rather huge 6.6Ah Endurance battery they used to do for halogen set-ups.
I sent mine off to Lumi and they did a conversion to stick it in a bottle, including custom length cables for £25 or so. They apologised for the cost, but explained that most of it was labour….
Give them a ring, I was well pleased with the service.
I have converted one of my cans to LED and am doing the other soon (hopefully this weekend). With both done I’ll have about 6hrs runtime with both on full blast so i am thinking of asking Lumi to split the battery into two instead of having the one HUGE battery.