Tuesday, February 7, 2017

Battery Failure Assessment

Last week, I had a very inconvenient failure of the battery in my truck.  I don't often expect things to fail -- my maintenance routine isn't perfect, but it's fairly solid -- so when they do, it's an unpleasant surprise.

At about 5:40 in the morning, I went out to start my truck and go to work like I do any other weekday. When I turned the key, I was rewarded with the rapid click of a low battery that couldn't spin my starter. I roused my wife and got a ride to work, but I was left scrambling to arrange transportation home and deal with a truck that needed attention.

The immediate fix for a dead battery is either a jump start or time on a battery charger. The way we park our trucks isn't exactly conducive to a jump start, and I didn't have the time for it that morning, so I plugged in the charger and hooked it up when I got home. An hour or so later the truck would start, but I still had a root problem to track down.

A dead battery is usually the result of some kind of a drain. The most common cause is a light or a stereo left on at a drive-in double feature. When I started the truck, nothing appeared to have been left on, so that got ruled out.

Old batteries can develop problems with holding a charge. Lead-acid car batteries average 3-5 years, depending on environmental and usage conditions. I replaced my battery sometime around Labor Day, so I could rule that out as well.

Diagnosing the Problem
That left just a few possible causes. Sorting those out is pretty straightforward, but requires a couple tools:
  1. Start with a check of the battery itself (I explained how to do this in an earlier post). As I said before, my battery is new. The posts are clean, the water is full, and the clamps are tight.
  2. After making sure everything is physically good, check to make sure that your battery is holding a charge and that your alternator is actually charging the battery. You'll need a multimeter for this; I use this one at work, and an older variant of this one at home. 
    • While the Milwaukee is simple and quick, the Amprobe is half the price and will do anything you could want a meter to do. 
    • A multimeter is a wonderful tool investment on the whole, as it will help with any number of projects around the house.
    • For those of you who are a bit scared or confused using a multimeter, next week I'll go through the basic functions of a meter and how they work. Stick with me on this, you'll do just fine.
  3. Following the instructions for your meter, set it to test 12 volt DC power. 
    • With the car off, check the voltage stored in your battery by touching one test lead to each post. 
    • If your battery is holding a good charge, you should see 12-12.5 volts. 
    • Anything below 11 volts indicates a serious problem.
  4. Now, start the car, and repeat the voltage test with the engine running. 
    • If your alternator is charging properly, you should get a reading of about 14.5 volts. 
    • Any reading more than a volt off of that indicates a problem you'll need to have addressed. 
    • My battery gave readings of 12.4 and 14.5 volts, so the system is working properly.
If I'd gotten low readings on the battery, I'd have taken it to an auto parts store and had them charge it and test it. If the alternator had given odd readings, I'd have pulled it and had it tested at the parts store, and replaced anything that testing showed as defective.

Why did my truck not start?
With all of my tests coming up negative, the question remains, what happened? The answer is twofold, and one of those folds is entirely my fault.
  1. The weather had been brutally cold for several days leading up to this failure. Cold does bad things to battery output, and I hadn't started my truck for a few days to keep it charged. 
  2. When I bought that new battery a few months ago, I gambled and bought one that was a bit lighter duty than I normally get, and this is the failure that I have to own. Car batteries are rated by Cold Cranking Amps, with more amps indicating a stronger battery. I normally buy 700-800 CCA batteries for my big trucks, but this time bought one in the mid-500s. 95% of the time I don't even notice, but when combined with the single-digit and sub-zero temperatures, the lighter battery just didn't have the gusto it needed. I learned a valuable lesson in false economy, and may look at buying a larger battery in the not-too distant future and swapping this one into my wife's smaller truck.


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