by mr_luke » Fri Feb 28, 2014 3:33 am
I wouldn't want to go too much smaller, capacity-wise, than the original, as the little TSes do seem to be a little short on sparks, if you want anything as luxurious as lights and motion at the same time. I seem to recall the original is 9Ah? If so, there are Cyclon gel 8Ah batteries on ebay for about a tenner which might do the trick? I assume you'll be dispensing with those pesky indicators, and you could look at LEDs for tail/brake and sidelights, and perhaps a halogen for the headlamp, which should all reduce the power needed. The big advantage of these is that you can mount them any way up, so they're good if you're lacking in space.
Any 6V coil with two terminals should work, provided it's intended for points, rather than electronic ignition.
I don't know about your budget, but I guess a Powerdynamo kit would solve all your problems, especially as it can allow you to run without a battery at all!