Okay. My motorcycle electrical system is giving me problems. I suspect it might be a pooped-out battery, but it could just as easily be problem elsewhere – an alternator that doesn’t charge or a short that drains the battery dry during downtime or something else.
Anyway, this afternoon I took the battery to the auto supply store to be checked out. I am pretty certain the battery HAD LITTLE OR NO CHARGE in it at the time. (This may be important; read on.)
The clerk pulled out a meter gizmo, clamped it to my battery with giant alligator clips and flipped the switch on the meter. The needle on the meter lept to the “REPLACE” zone.
Now, here’s where I have a question – which obviously the clerk was unable to answer to my satisfaction, but I’ll save that gripe for the Pit.
Was the meter telling me that the battery HAD NO CHARGE (i.e. it was a “drained” battery), or was it telling me the battery WOULD NOT HOLD A CHARGE (i.e. it was a “bad” battery)? To me a drained battery may be a perfectly fine battery that just needs to be recharged; a bad battery needs to be junked.
The reason I ask is that the last time I had a (car) battery checked, the guy hooked it to a meter (while it sat under a clear plastic hood) and told me to come back in an hour for the diagnosis. Presumably the device needed to charge the battery before it could determine if the battery would hold the charge. This made a lot of sense to me.
But maybe there are better meters out there that can tell if a battery is shot regardless of the state of its current charge. I don’t know.
My limited knowledge says that you can’t reliably tell if a discharged battery is no good until you have attempted to charge it. Perhaps there’s some sort of test equipment that purports to be able to do this, but I think you should put the battery on a trickle charger overnight before having it tested.
Yes, the guys in auto stores are often morons. That’s not to say that the customers aren’t, occasionally.
In the past they could test to see if the battery was bad. I don’t think they can do that now with modern sealed batteries.
In many cases once a battery goes all the way dead it will not be able to hold a charge again. (that can happen if you leave your lights on for example) If you know of a mechanic that specializes in electrical problems that’s the best place to go to get it checked out.
It may very well be your charging system. Or a short in the system.
A battery charger does not cost that much, and can be a useful tool in your collection. But it does not solve the problem.
Are the cells in the battery accesible? You can get a simple tester that checks the specific weight of the water in the battery that will tell you if it has any life left. It’s a syringe with a bulb on the end to pull the battery water up into.
Add one of these to your toolbox, they are really cheap. Also add a multi-meter. Even a cheap one.
Can you bump start the bike?
In answer to your question, I have to say that it sounds like the clerk just put a multimeter on your battery. Just measured the volts left.
Nowadays there are very sophisticated battery testers that do not require the battery to be fully charged. My Snap-On catalog shows one that states it can test a battery with as little as 1.0 volt charge. However, these tend to be digital devices and your description of a needle going to a “replace” zone makes me doubt that it was that type of tester. In your case, it might make sense to charge the battery and have them retest it.
I’m certainly not an expert on batteries. (Who is? It’s very difficult to find scientific data on the subject.) But I get the feeling the guy was just trying to sell you a new battery.
As you suspected, sticking a voltmeter on a battery will give you an idea of the charge on the battery, but it won’t tell you about the health of the battery. It could be a good battery that is in a discharged state.
Here’s what I would do:
Attempt to charge the battery with a battery charger at a rate of C/10. Will the battery take a charge? If it won’t take a charge the battery is probably bad. If it does take a charge proceed to step 2).
Once the battery is charged, perform a load test on the battery. It’s a pretty simple test:
a. Measure the open circuit voltage of the battery. To do this, just stick a voltmeter on the battery and measure the voltage. We’ll call this voltage V[sub]OC[/sub].
b. Get a load of known resistance. (An electric heater works well.) We’ll call the load resistance R[sub]L[/sub]. Connect the load to the battery.
c. Measure the voltage of the battery while the load is still connected. We’ll call this voltage V[sub]L[/sub].
d. Calculate the battery’s series resistance (R[sub]S[/sub]). Use this formula:
e. Compare your value of R[sub]S[/sub] to the manufacturer’s spec. If your R[sub]S[/sub] is much higher than manufacturer’s spec the battery is probably bad.
An even better method of measuring R[sub]S[/sub] is to use two loads of different resistances. Email me for the equation.
He was probably checking the load test of the battery, as I have asked it to be done & they show me the test. In other words, what would happen when you try to use the battery. A fully charged battery shows fully charged & if it that can’t complete a load test it needs to be changed.
Find out how old your battery is too:
“You can usually find a small decal on the side of the battery container giving you the month and year the battery was shipped out of the plant. The letter corresponds with the month, starting with “A” for January, “B” for February, and so on. The number represents the year with “9” standing for 1999, “0” for 2000, and so on. A9, would be January, 1999. C0 would be March, 2000.( The letter “I” is skipped so the letter “M” would be December.)”
The gizmo that the clerk hooked up is almost certainly a load tester (a self-contained version of what CrafterMan described). Note that this tester is of no help if the battery has not been recharged. It is intended to measure the battery voltage under load. (See CrafterMan’s post).
Recharge the battery (at the lower rate) and try the load test again, bearing in mind that it helps to know what you are testing to understand the results. You now know, maybe you can help the clerk.
If you charge a battery at too high a rate, you risk overheating the plates, which causes the lead peroxide paste on one plate (I have to admit I forget which) to flake off, shortening the battery’s life.
See Secrets of Lead Acid Battteries by T.J. Lindsay.
Did the clerk know it had little or no charge? That wasn’t made clear. If he knew, then yes, he’s a nugget. If he didn’t have that bit of information he may have assumed it was charged, and went ahead with the load test. I’d fault him for not popping a multimeter on to check, but at least that isn’t nefarious.