Motorcycle Battery Issue


#1

I recently bought a motorcycle and after I had ridden it home, the battery died the next time out. I replaced it and two rides later my battery died again. After charging the new battery, I had 13 volts going to the battery and my service manual says that the charging voltage is 14 volts. I took it to a dealer to have the magneto resistance tested to see if it passed spec to see if the magneto or regulator is bad. The dealer told me the battery they sold me 2 weeks ago was bad, replaced it under warrenty and charged my $100 for labor. Do you think I had a bad battery like the dealer said or that they don’t actually know what is wrong??


#2

Since you didn’t name the make or model of the motorcycle, or tell us whether it’s new or used, it’s really hard to say.

It’s possible to get a bad battery. I have to assume the dealer tested the battery, but, again, you didn’t tell us.

Does the bike start now?


#3

New or used bike is useful info. Most motorcycles do not have an alternator. They have a stator that is somewhere on the motor mounted to a spinning shaft. A bad stator can be very labor intensive to replace. Lots of folks sell a bike used rather than replace the stator. Hopefully your battery was bad because a failing stator is often a major repair on a motorcycle.


#4

They charged you $100 labor to replace a bad battery that they sold you, did the name of the dealership end in “of Beverly Hills” . Seriously you need to find a new place to get you work done.


#5

Actually, almost all motorcycles have an alternator, it’s just not an automotive style excited field type of alternator and it’s not so much that they are labor intensive to replace as it is that motorcycle parts tend to be stupid-expensive.
I’d rather replace the stators on three Yamaha SR500 motorcycles than replace the alternator on a single Geo Metro, provided I have the special flywheel pulling tool needed to remove the flywheel so you can access the stator.

A lot of motorcycles, especially the larger ones actually do have automotive style alternators. My ZRX1200 for example. The alternator is on a jackshaft behind the cylinders instead of on the end of the crankshaft, keeping the four cylinder engine narrow. My old Honda 550 four had an alternator on the end of the crank and it was unique in having a stationary field coil that fit closely inside the rotating rotor thus eliminating the need for brushes. My old KZ 400 also had this alternator design.

Some older bikes used generators. The old iron head Harley Davidson Sportsters had a gear driven generator on front of the engine. Old Moto-Guzzi V7 touring bikes had a belt driven generator on top of the engine. Yamaha made a 125 cc two stroke single back in the '60s that had a generator on the end of the crankshaft that doubled as a electric starter.


#6

Another point. Don’t be too quick to blame the stator. Most bikes that use a permanent magnet (magneto) type of alternator have the diodes and regulator in the frame somewhere, not integral with the stator.

When I had the KZ400, I found myself with a dead battery on a trip and I found that the chain sprocket was rubbing on the wires and wore through one of the wires going from the alternator to the regulator/rectifier. A soldering iron, some solder, and some electric tape, and carefully re-routing the wire had me on my way again.