What speeds were you riding and what conditions of traffic/rpm and time were you riding?
If wired up correctly and your battery runs down, you should be running directly from the stator with no power support from the battery, this should easily run a standard lighting set up. It could be something as simple as a wiring error or time for a new battery as it's simply not holding charge, but as I say it should run from the stator in that case. If you check all the above and you still have issues, then it sounds like your stator, but check the above first
I hope this helps
Mike
