My motorcycle has a bum battery, I think. It can’t seem to hold a charge.
Trouble is, I’m not really 100% certain the battery is at fault. I brought it to a Pep Boys (which sells motorcycle batteries, btw) and asked if they could test it. “We don’t have a tester for MC batteries,” the guy told me. Ugh!
So, can I test it myself? I have a pocket voltmeter and a trickle charger. (Note: I removed the battery from the bike which is parked far away, so I hope I won’t need the bike in the testing procedure.)
4 years ago when I first purchased this battery, I had several questions about the initial battery charging procedure, and I got some terrific advice from several battery-savvy Dopers like Rick. (It was so good I printed it out and saved it.) So I’m turning to you guys and gals again. Spare me the trouble of lugging this friggin million-pound thing all around the planet on my bicycle looking for a place with a MC battery tester.
Can’t test a motorcycle battery? :rolleyes: Boy the kids they are hiring today.
Getting back to the OP, yes you can test a battery’s state of charge with a voltmeter.You can also determine if the battery will take a charge or if it has a dead cell. You cannot test a battery’s ability to deliver amperage with a voltmeter. Since this is what you need a battery to do (deliver amperage to start your car or bike) you will be unable to do the most critical test. However if the battery fails one of the tests you can do, then you know it is bad. If it passes all the tests you can do with a voltmeter, it may still be bad.
Start testing with your battery not been used, or charged for at least 4 hours.
Test the voltage across the battery (either disconnect a battery cable, or make sure the motorcycle is OFF)
12.60 Volts or above (fully charged)
12.45 Volts 75% charged
12.25 Volts 50% charged
12.00 Volts 25% charged
11.90 Volts or below DEAD
If you are having trouble starting you bike and the above test shows 12.4 Volts or above, either you have starter issues, cabling issues, or your battery is bad.
Now attach your battery charger. Remeasure the voltage with the battery charger running. It should be about 1.2 volts above the reading you got before. Allow the charger to run until you see 13.92 Volts or above. Disconnect the battery and allow it to rest overnight. Remeasure the voltage, it should show 12.6 Volts or more. If the voltage has dropped below 12.6 Volts you have a dead cell, replace the battery.
Assuming your battery has passed everything up to this point, start the bike and run it in neutral at about 1500-2000 RPM measure the voltage at the battery. It should be at least 13.8 Volts and probably not more than 15 ish (different companies have different high voltage cut offs). If with the engine running you are getting less than 13.8 Volts you have either cabling issues, or alternator issues. Last alternator check, set the meter to AC Volts turn on the headlights (high beam) rev the engine to 1500-2000 and measure the AC voltage at the battery. It should be below 0.4 V AC. If it above that you have a bad diode in your alternator.
If you have to take the battery back to Pep Boys some things to keep in mind:
I bought a battery a while back from PB (Odd ball size for some car) When I got home, it would not start the car. I tested the open circuit voltage (first test listed above) the voltage was 10.8V ! :eek: The damn thing had sat on the shelf for so long, it had self discharged to the point it was dead. So if your battery was bought wet (you did not have to add acid) it could be old and have issues that prevent it from accepting a charge (called sulphation) If you have to warranty the battery, before you take the new one home, measure its voltage. If it is below 12.2 V don’t bother. Tell them you want a battery that has a charge. If PB is not going to maintain their stock, I have no problem making sure I get a good battery. If it is above 12.2 but not up to 12.6 put it on your charger before you install it.
If they tell you they cannot test a motorcycle battery tell them it is just like a little tiny car battery. It has either an amp hour rating or a cold cranking amp rating, and tests just like a car battery.
If the above test show a cabling or starter issue, get back to me and we can start running it down.
Rick’s instructions are pretty good, but left out one possible problem.
If the battery is losing its charge while running the bike, it could be an alternator or a regulator/rectifier issue. I’ve seen this problem on a couple of bikes. The R/R takes the AC current generated by the alternator and coverts it to DC to charge the battery. It also regulates the charge to prevent over-voltage. If it goes bad your battery will not be charged properly by the alternator.
