Load testing a battery
 

Found a good video on this as winter's coming on and helps show if you have good battery or one that's possibly getting weak. Better to check one than to be stranded somewhere. Shows using a Fluke meter with min/max voltage setting,but a reg meter can help. Just need a good set of eyes to check what the voltage drops to while under a load while starting,etc.

Good post OPT. It should probably be a sticky. My meter doesn't have that min/max button but it sure is a nice feature to have.

Great, as always, information. Thanks again OPT for a quick and easy test.

Of note: digital multimeters are very less accurate in the bottom 10% of any range, so try to avoid a range selection that will put your displayed result in the bottom 10% of the selected range.

Also if you don't have a min/max selection (typical capture rate of 250 µS) on your meter and your machine starts very quick you may want to leave it out of run (so it doesn't start) during this test to get the "low" reading. DMMs without the min/max typically don't have a great sample rate/response time and you could get a false reading if the engine starts quickly.

Switching the emergency switch to off cuts the ignition and power on Polaris atvs,but works great this way on some other models and street bikes that still allow the starter to engage but no ignition like the kill switch on my my old Honda.That's how I was able to load test my Yuasa battery. After 6 years it showed weak after a couple starter revolutions and I finally had to replace it last week.But one way you could bypass this on Polaris atvs is to have leads on the battery,key off and jump the solenoid. This can give you a good idea as to voltage drop without having to have this 300 buck Fluke meter. 5 to 10 seconds can show you what the voltage drops to pretty quick. Most instructions say a battery should stand this load for up to 30 seconds,no dropping below 9.6 volts,but we didn't even have to use our load tester that long at the shop on batteries before we knew what shape they were in. Batteries in good shape would heat up the load tester real quick if held on for more than 10 seconds.

Voltmeters and load testers are great tools to get a down and dirty reading on battery's health but for starting, what you really want to test is cranking amps. Plenty of batteries that test fine on voltmeters and under load but still can't start an engine or are slow to crank. Load testers test the healthiness of the cells, i.e. state of charge of the sulfuric acid used as electrolytes in the cells, but don't tell you much about the healthiness of the plates that conduct the amps needed for starting. You'll need to perform a conduciveness test for that with something like this...




Just this morning, I had the battery tested on one of my vehicles and under load, it tested great but given that it was slow to crank since the temps dropped, I had them measure CCA as well. Battery was rated for 600 CCA but only tested for 280. I'm due for a new battery.

So if you get a battery that tests "good" under load and still won't start your engine, before you go chasing gremlins, try running a conduciveness test, or at the very least, hook up a comparable battery that you might have in another vehicle and see if it makes a difference.

That's a great find and at a very reasonable price. I don't have the disposable income I used to have (retired) so I'll have to wait until my current barn-find stops nickle and dime'n me and I can save a few bucks to get one. That'd be handy to have around the farm. Thanks for the post.

In the meantime, you could take the batteries to an auto parts store. Some perform conduciveness tests as part of their free battery checks.