Battery power (voltage) level drops below level to crank engine

josiah

Full Member
Joined
Jan 5, 2007
Messages
124
Points
16
Make
toyota
Model
camry
Year
1987
Miles
235,000
Engine
4 cylinder
Recent problems and fixes
1) 2020. Problem: Brake lights ON ALL THE TIME.
Fix: Replaced brake light switch cushion with help from Mobile Dan and others. Brake lights fixed.

2) 2021. Problem: Brake lights NOT coming on.
Fix: Determined to be Light Fail Sensor malfunction with help from Mobile Dan and Nickb and others. Jumped sensor. Brake lights fixed.

Current problem
Battery power is dropping below level to crank engine.

Tests I have done
1) Each time after the battery level has dropped I have used battery charger to return it to full charge.
2) When I reinstall recharged battery in car it has started the car easily.
3) Please note: If I disconnect the negative battery cable for days or weeks the battery does not lose power. And it has consistently started the car easily, obviously after I have reconnect the negative cable.
4) Some days I have left both cables connected and started car at appx 4 hour intervals with no problem.
5) However, one day with battery connected, I tried to see if it would crank after 7+ hours and it did NOT. So around 7 hours or more is he breaking point.
6) I did battery test I found online in which you check the battery voltage (A) before crank (B) during crank and (C) after start. In the test you want to see if there is a significant drop in voltage during crank. My reading were 12.8, 10.5 and 15 respectively. So the battery passed the test.
7) With battery connected I have walked around car, and sat in car, after dark to see or hear if any component could be on and draining the battery. I have found nothing.

My further thoughts
1) I think the battery is fine. It passed the voltage test. And when I disconnect the negative cable it holds it's power. Please let me know if my logic is flawed.
You may wonder why I have not taken battery to local parts store for a free battery test, the reason is lack of confidence. I previously lost a good battery trusting in a store's free test.
2) I don't recall having this problem until after jumping the Light Failed Sensor but it may be just a coincidence. But I do not understand how that could drain the battery.

Any advice would be appreciated.

Thanks Joe.
 

billr

wrench
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Messages
7,444
Points
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What DC amperage ranges do you have on your electrical meter? You need to check what the current drain is when the car is supposed to be inactive. There are many things that still could be "on" that you can't hear or see visually.
 

josiah

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Messages
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Points
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billr, Thanks for the reply. My Sears Craftman digital multi meter lists the following DC range settings->A DC->(2m, 20m, 200m and 10). However (1)when I rotate the selector dial it stops and will not allow me to select in the A DC range (also A AC is also blocked) and (2) the meter lists 10A and MA jacks, but the jacks (or ports) are covered preventing insertion of the the test probes (red and black).
The only ranges I can use appear to be CAP, OHM, V DC, V AC and a sound symbol ( which I think is continuity).

grc, Thanks. Please see my original post above, under "Test I have done", #6. Is that an adequate battery test? If not, then how I do a Load Test?

By the way the battery has been sitting in my garage after I fully recharged it. Based on my previous tests it should start the car easy.

Thanks for your help, Joe
 

grcauto

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May 29, 2014
Messages
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Points
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That test is not adequate. A load test will usually draw about 250 amps and see if it holds at 10.5 or above.
 

billr

wrench
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Messages
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Points
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My understanding is that the battery will hold a charge fine if disconnected from the car and will crank it fine when re-connected. OP, is that correct? If so, the battery is probably fine. The problem is more likely to be a (greater than normal) parasitic drain in the car's electrical system.

Finding such a drain without a clamp-on ammeter can be done, but is quite a bit more tedious. You will need to step up toward the $100 range to get a clamp-on that will give enough resolution in the lower amperage range. You need to be able to see drains in the .1-1ADC range.

A simple load test is to leave the headlamps on for 1/2 hour or so, with engine not running. After that 1/2 hr the battery voltage should not drop from 12.6V to much lower than 12V, and should recover to nearly 12.6V once the lights have been turned off again for another 1/2 hr.
 
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