Using a Multimeter to Check Voltage
The old workhorse Honda CRV has been a tad slow turning over lately on cold mornings and a recent ‘who left the lights on for ten minutes?’ left us without enough battery power to even turn the engine over at all. Que random mad clicking and flashing dash lamps… Oops!
Now, we’ve been running around in the Honda for nearly four years and the battery looked far from new when we bought it, so it doesn’t owe me anything really. It’s often quoted that 4 or 5 years is a good life for a car battery.
But being me I wanted to double check. So I connected up my trusty multi-meter to see what’s going on… Red to positive and black to negative.
Now you might think that 12.4V is not too bad, but considering the car had just done a long journey before retiring for the night, I would have expected a little higher voltage, 12.6V or at least 12.5V. So that’s the first indicator of a problem, the battery is not 100% fully charged.
Voltage problems are usually one of two things: the battery will not hold a charge or it’s not receiving a charge from the alternator (the cars electrical power plant). So the second test we can do is to check the alternator. Start the car and measure the running voltage. And in this case I had 14.7V which means the (much more expensive to replace!) alternator is putting out a healthy voltage more or less guaranteeing the fault is in the battery, phew!
The first two tests show there might be a problem with the battery and there is one more test you can do at home and that’s a starting load test. You really need a special tool to properly load test a battery and incidentally most auto stores will do this for you freely. At home you can only do a starting load test using a multi-meter. Connect up the multi-meter and ensure the probes will withstand the wobble of a starting engine.
Position the multi-meter where you can see it from the driver’s seat (or get someone else to crank the engine for you) and crank the engine whilst keeping a careful eye on the multi-meters display. Look for the lowest voltage it displays. In my case the lowest voltage was 9V. This is a little too low. I’d have expected around 9.5V or so.
If you know how to disable the car and prevent it from starting (by removing an ignition or fuel pump wire) you’ll get a better test as you can crank the car for 10 seconds or so and get a better idea of the effect of the load on the battery. If you don’t know how to do this, just do the test till the car starts, it’ll still give you an idea.
In conclusion the battery on my Honda is not totally dead yet, but the test results show that it might be shortly. And with the cold weather we have right now, replacing it sooner rather than later is a good idea (I picked up new one yesterday and it’s in the boot already actually!). In the meantime you have a set of jumper cables in your car yes? (good idea to always carry a set IMHO….). Don’t forget it might not be you that has a flat battery and it’s always nice to help someone else out isn’t it?
Keep an ear open when you start your car for the first tell tale signs that your battery might be slowing down and you’ll potentially save yourself from getting stuck somewhere with a dead battery. Especially important for all of us automatic drivers as you can’t bump or push start an auto!
Stay fully charged!
Ian
