How to remove "surface charge" to accurately test battery?

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Dec 1, 2014
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I have a TopDon BT200 battery tester. To get the most accurate testing of my battery, TopDon support says, "You are not recommended to test the battery immediately after it is fully charged. There may be floating electricity causing inaccurate test results. Please let the battery sit for a while and then test again."

I'm not sure what they mean by "a while", so here's what I do.

With the motor off, I first disconnect my trickle charger and then turn on the headlights for about 5 minutes. Then I test my battery condition with the TopDon.

Does this sound like a reasonable way to determine my battery condition? Should I wait for more than 5 minutes before testing, or...???

Thank you,
Ed
 
My tester recommends turning high beams on if it detects a surface charge, unfortunately it almost always fails to detect that action- not sure if led lights dont draw enough or it’s just flakey. I would think a minute or two max would do it.
 
Years ago I designed a handheld battery tester for 70amp hour AGM deep cycle batteries. We had about 6000 of these batteries that would be charged and then deployed across 10+ square miles. To remove the surface charge, I would run 5 x 500ms 50% duty cycle 30amp loads on the battery. For a surface charge, running your headlights for 5 minutes seems to be way too long even for a larger starting battery in a car. Headlights for 30 seconds is plenty for the surface charge.
 
Do these new LED headlights use a lot less current than in the past? Is a few seconds enough?

I just wait like 30 minutes and test.
In my case, I have a 2019 Toyota Tacoma which does NOT have LED headlights (that was the 2020 models, and newer), and I have the original, FLA battery that I'm referring to.

Ed
 
I usually wait overnight to dissipate the surface charge but if you want to shorten the wait then simply monitor the battery voltage every hour. When it stops falling then the surface charge has dissipated. It is going to be hours rather than minutes.
 
I turn my lights on long enough to pop and open the hood, then shut them off. My ancel seems ok with this.
 
I used to wait for 24 hours after charging, but I was getting misleading results with that time based method. A more quantitative approach I saw mentioned online is to remove 1% of the battery capacity. With my 55Ah battery I connect a 75W halogen bulb for 5.5 minutes, then wait for 20 minutes before testing the battery.
 
The Ancel BA101 tester claims it will automatically sense a surface charge and prompt to turn on your headlights for 10 seconds, then turn them off before resuming the test.

I have seen other testers ask you to turn on your headlights for a longer period, say 30 seconds, then wait up to 10 minutes for the battery to recover, then test.

Seems there are a lot of different test protocols. I guess as long as you are consistent in your method you will have results you can compare against previous tests.
 
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