Originally Posted by HobartDave
Hey guys. Sorry to bring the subject back to bikes, but I'm wondering if any of you are lighting/battery experts?
I've got a cateye double halogen setup, with the brick (lead acid) battery.
Have any of you swapped out the battery for something lighter, and with a quicker charge time, and longer burn time?
Lithium is THE WAY TO GO. It's like putting Carbon bits on your bike.
Seriously, Lithium has many pros. Extremely high cycle life, linear voltage discharge, very high energy density (lightweight), robust. It also has some nasty gotchas for the unwary.
You could go with 3-cell LiPoly or LiIon. LiIon is better for low current apps such as lighting. 3 series LiIon cells would give you a nominal terminal voltage of 10.8V.
Try to get a pack around 5AH capacity. Expect to pay around $200. To charge it you WILL ABSOLUTELY need an intelligent charger. I suggest the Novatech B8070 which will auto charge LiIon and LiPoly in both serial and parallel configurations. This charger is around $50 at good model stores, say HStore (do a google search).
Try to get a battery pack with a cell breakout connector on it (HStore has them). The Novatech charger is one of the few chargers which is capable of using this connector to parallel charge the cells. Expect a charge time of about 2 hours (no less with any Lithium chemistry - it's a constant voltage charge profile).
LiIon is more robust than LiPoly but has a higher impedance and cannot deliver as much current. About 1C is it's safe limit, so your 5AH battery will deliver 5A, which should light up the road ahead, and the next 'burb too!!
LiPoly can "kick ass" seriously, around 20C discharge rate. A modern 5AH pack ought to be able to deliver 100A if it's kept cool. Competitive modellers do this all the time. Really good if you want a searchlight on your bike!!! The disadvantage of LiPoly is a capacity loss of about 50% over 2 years, independent of it's amount of useage.
In either case, if you are cavalier about charging series connected Lithium chemistry batteries they will catch fire and burn your house down. Seriously. This is a big deal in modelling circles and there are many stories of modellers burning down their houses, workshops, cars, etc. You can't put the fire out either - water makes it burn better!!!
The absolute safe way to charge is to break out the cell connections and charge the cells in parallel. The charger I suggested will do this. A fire WILL NOT occur if you use this charger.
Any modeller doing competitive electrics, heli or aero, should be able to help you - the modellers have got this technology nailed!!
Hope this helps.