That’s how I do it, including the recommendations above to unplug the battery charger before removing the cables at the end of the procedure. I also connect up a DVM to measure the battery voltage while it charges to better monitor the situation. My charger has a 12 v/6 v switch, and a 2A/6A switch, so before starting this procedure I make sure the charger is set up to charge at the 2A rate at 12 volts. I don’t leave the cables connected for more than a few minutes after unplugging the charger, as that could partially discharge the battery.
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Chargers are more expensive than they used to be but still they are fairly cheap. No reason to continue using an old relic. Can’t count the number of times I’ve needed one. As a teenager I’d have to take the battery out and take it down to th3 shell station. We never had a charger.
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Sounds like my battery, partially discharged most of the time. Wasn’t aware that can lead to permanent damage.
Good article, thanks.
From Maximising Battery Life | Century Batteries
Measuring voltage across battery.
- 12.6V volts or above - Your battery is healthy and fully charged. No further action is required.
- 12.5 volts - Your battery is at a healthy state of charge, but we’d recommend re-checking it within a few days to ensure the voltage hasn’t dropped any further.
- 12.1 - 12.4 volts - Your battery is partially discharged and should be recharged as soon as possible, using a suitable battery charger. The lifespan of your battery will be moderately affected if it remains within this voltage range for extended periods of time.
- 12.0 volts or below - At 12.0 volts your battery is considered to be fully discharged or ‘flat’ and should be recharged as soon as possible. The lifespan of your battery will be severely affected if it remains within this voltage range for extended periods of time.
I charged the battery yesterday and then checked it with a voltmeter. Measured 13.6 volts. Battery appears good. Plan to recharge the battery every three months or so. Yes, it has battery caps, as Rainflurry said. Thanks to all who chipped in their knowledge.
That’s not quite an accurate method
What you measured included the surface charge, which needs to be removed first
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Even after reading SmartGauge Electronics - A simple explanation of "Surface Charge" I don’t pretend to understand it.
You just work it a little like starting the car and going for a little drive. Then check the voltage. But voltage is only part of it. You need to know the capacity in terms of the cold cranking amps available. That would be another test equipment. I can’t explain surface charge. It is just in my head. Maybe like getting splashed with water and then soaks through your clothes.
What I have learned as a non engineer is that I dont have to understand something, just follow directions.
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Exactly right.
Maybe these analogies will help anyone with the concepts:
Surface charge is like a powdered sugar donut. You can have lots of powdered sugar on top of the donut but not all of it sticks. Tap the donut and some easily falls off. It is loosely coupled and not really embedded in the donut. As soon as you put a small load on the battery, that surface charge will dissipate and you’re left with the “embedded” charge.
Voltage is like measuring the height of water in a bucket. Capacity is the amount of water in the bucket. A 12" bucket full to the brim with only water is at full capacity. Now empty it and fill it halfway with fine stones before filling it with water again. The height of the water is still 12" but it’s only half full of water. It has 50% of the capacity that the empty bucket originally had.
Simple analogies that, like any analogy, is not 100% perfect explanation but perhaps helps to understand the concept…
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Thank you. I’ll remember that.
The battery voltage immediately after charging doesn’t provide much info. Let it sit overnight, then tell us what the voltage is.
I charged a battery the other day for 4 hours. It measured 12.9 volts immediately after charging. 12.3 volts after sitting unused 12 hours .
Or you could remove the surface charge in a few minutes
If no way to test it (for whatever reason), you can just turn the headlights on bright for about 15 minutes, then back off, if the vehicle still starts, battery probably still good, a battery should have a reserve…
Thinking about it, this might be different with LED/HID lights depending on how much power they pull from the battery… But has always worked pretty good on standard halogen bulbs…
My apology’s, I was talking about checking the battery in general without going to a parts house or having a proper tester in general…
I was not referring to the surface discharge part…
But that link, it s a good read and should help others, thanks…
Update: I charged the battery again for 2 more hours at the 2A rate. 12 hours later, it measured exactly 12.6 volts. Perfect. Job done.
Stop right there!
Forget charging, take it back to Walmart and let them charge/test it…Has to have at least a 12/mo warranty…you may get a new battery for free.
Take the battery out of the car, take it to walmart and leave it with them. They’ll charge/test it and you can come back later for the results.
Exactly what I did the next day. The battery tested good.
Would it be due to the brief charging I’d done the day before?
My calendar now reminds me to charge the battery every three months. I just make too many under-2 mile trips.
That is a lot of work to recharge a battery. Rather than let someone who I don’t trust to fool around with my battery, I’ll recharge it myself.
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You’re not taking it to them to “recharge the battery”; you’re letting them tell you it is/isn’t a bad battery.
#1 - Dealers are, typically, not your friend…
You can buy a battery tester on Amazon that is really pretty good and not very expensive; well worth owning. I test my batteries every 3 months and keep a log.
Also, if you can easily, keep a battery tender hooked up as much as possible. I have an attached garage so before I go to bed I hook up the tender (pig tail in grill)…it charges to full and holds it. I get 7 to 10 years out of my batteries. My motorcycle battery, notorious for short lives, is now 6 years old and still cranks over my big Harley. It is testing at reduced CCA, but still enough to get the bike started.
Don’t buy a cheap tender. Buy a good one, does a better job and lasts forever.
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