I have the following setup for solar power, which worked well until recently:

solar panel <--> solar charge controller <--> small (car) battery <--> converter: 12V DC to 220V AC <--> my power tools

Last year, on a full battery I could power heavy tools such as a belt sander for many hours before it ran empty. But now, when I use power on a seemingly full battery (see video below, the battery indicator is full at the start) and 13V on the battery which should be good, the voltage drops immediately after starting the tool - and the battery indicator drops to zero. The converter beeps (low voltage warning). After a few seconds, all power supply stops. When I wait about half a minute, the battery indicator jumps back to "full" again, and I can use the drill for another few seconds until it drops again.

What could be the case here? The battery seems to have enough liquid. My initial thought was to replace the battery, but this strange behavior with the indicators on the solar charge controller makes me think the problem might be in another component.

Video of it happening:


  • 2
    \$\begingroup\$ Battery went flat in the dark season and failed. \$\endgroup\$
    – user16324
    Mar 17, 2020 at 15:47
  • \$\begingroup\$ @BrianDrummond What does dat imply? Do I have to replace the battery or refill it? (I am a complete beginner with batteries etc. so I may be asking dumb questions) If you think you have the solution, please write it in an answer to the question and I will accept it. \$\endgroup\$
    – Hacktisch
    Mar 17, 2020 at 16:12
  • \$\begingroup\$ batteryuniversity.com/learn/article/…. Replacet I think. \$\endgroup\$
    – user16324
    Mar 17, 2020 at 16:33

1 Answer 1


As @brian-drummond commented, the issue was in the battery and replacing it by a newly purchased one solved the problem. The battery was fully charged during winter however, but maybe the winter cold damaged it.


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