Okay nerds, help me out here. My motorbike runs a 35w headlight off a 3Ah battery, but the problem is that it takes about 2 minutes to completely flatten a charged* battery.
So I did some calculations: a 35w globe at 12volts draws 2.9Amps ( ie. 35watts/12volts = 2.9Amps). The battery is a 3Ah and should therefore be able to run the headlight for about 1.03 hours (3Ah/2.9Amps = 1.03 hours).
Does this mean that if I was to take the battery out, sit it on a bench with 2 wires connecting the globe from the headlight, that it would power the globe for ~1 hour? Because I've tried that and it only powers it for a couple of minutes before it goes flat.
And yes I've tested the battery and it holds charge at 12.8volts, and when the engine is running the charging system is operating at 12.8-14volts. So everything seems fine, but the battery just dies in the arse when I put the headlight on.
Any suggestions? I'm taking the battery to get it tested tomorrow. Is it possible that the battery could hold 12.8volts of charge but have little or no amps?
*I'm guessing it's fully charged after leaving it on the battery charger over night.