Quickest solution would be to get some new bulbs & get your battery back to Lumicycle for servicing. I think it would be cheaper than replacing it (unless it’s completely dead). Give them a ring, they are very helpful.
I wouldn’t get your bulbs from them though. Just Google MR11 halogens and go from there.
The other route would be converting to led, which if nothing else will greatly improve your runtime. Chances are they will be brighter as well.
There is a long thread on here about it if you search. I converted one of my cans (and a mates as well) using a Cutter led & optic, a driver from eBay (‘black cat tech’ on here or ‘teapot’ on eBay), my own heatsink design & a new switch from Maplin.
Both lights on full blast lasted 7hrs 20 with the endurance battery as opposed to about 3.5hrs with the halogens before (20/12w).