Topic: Battery dying while running. :(

[aaverett]

I took my '74 CB350F for a killer night ride the other night when about an hour in, my headlight stopped working. Before I left for my ride, I put it on a trickle charger and got my AGM battery up to 80% capacity. Now the previous owner put some super-sonic headlight in the bike, which I believe to be the culprit because when the battery does get low and the headlight stops working, I can turn the headlight off for a few seconds while riding and then flip it back on and the light will work again for a few seconds...  I just charged my battery to 100% and took it to O'Reilly and they said the battery is good. So I brought it home, threw it on the voltage meter and took some notes. When the bike is off it sits at 13.1v, when it is at a smooth idle, it sits at about 12.4-5v, when I rev it at 2500, it sits at about 12.7-8v and at 4000 it sits between 13.1-3. I let the bike idle for 20 minutes and the battery drained from 94% to 9% with the headlight on. I know basically nothing about electrical, so I really have no idea what is going on. Any insight would be awesome! Thanks.

[RJ CB450]

Hiya, sorry to hear about the issue.  It seems like it is a little low.  Could be your coil.  Checking the 350, looks to be similar to my 450 for charging system.  Magnetic on the rotor, then coil outside with a series of windings.  Possibly one of your windings could be poor or a bad connection.

I do not think anything is burned out because you still get some charge, just not enough.  As for the battery draining, idle it does drain slowly since until it gets up a bit in rpm, it does not meet the charging demands.  At this time, I do not have handy what the resistance for your coil should be, but start with using some electrical cleaner and check your connections and wires for the alternator system just to be sure it isn't just a loose or corroded connection.

[flybox1]

Honda electrical systems don't recharge the battery until the rpms are above 2500 or so....so yeah...after a 20 minute idle, your battery will be drained.  Even more so with a headlight on.

[dave500]

see what wattage is written on the headlight globe.