My wife "Bash" took her Bashblaster light for a ride.
She came up with a very smart solution for attaching the battery:


It's a water-resistant iPhone armband holder.

Anything from a 1-cell to 4-cell battery will just drop in there.

Note the high mount for the light- she mainly uses it for ultra-running and 24hr orienteering, and likes it high on the headband. She has a 6-day nonstop multi sport race in Patagonia upcoming, so I'll be setting her up with a lot of batteries, and needs to be able to change them easily in the dark, cold and rain.