I have 12v calcuim+ battery was on my car but now it is almost dead (8.9v) I bough solar panel and charge controller to charge it.

i put it in the sun for two days and now it is 10.5 volts but still dead as it didn't charge yet.

i am not sure is it effective way to keep it for another few days or it is not even possible to charge it?

i have seen the questions here and over the internet all the batteries were not dead and also i didn't see the calcuim + battery

The solar panel is 50W

thank you all.

  • \$\begingroup\$ I haven't seen any test results or datasheets. The PV must be too tiny, or perhaps a bad cell \$\endgroup\$ Jul 7, 2020 at 20:20
  • \$\begingroup\$ The solar panel is 50W @TonyStewartSunnyskyguyEE75 \$\endgroup\$
    – Mhd Ghd
    Jul 7, 2020 at 20:25
  • 1
    \$\begingroup\$ insufficient details..... \$\endgroup\$ Jul 7, 2020 at 20:30
  • \$\begingroup\$ Please provide the part number of the battery and solar panel. \$\endgroup\$
    – Drew
    Jul 7, 2020 at 20:32
  • \$\begingroup\$ Silver-calcium lead-acid batteries don't like not being fully charged. If your car doesn't supply a high enough float voltage for it--higher than for a standard lead-acid battery--then it's probably dead. 8.9 volts sounds worryingly low, but I'm not an expert in lead-acid chemistries. \$\endgroup\$
    – Hearth
    Jul 7, 2020 at 20:32

1 Answer 1


My experience from 2007 thru 2021 is that a solar panel with a protective inverter device that shuts off at 13.8vdc can charge "dead" batteries, when a typical modern 120vac battery charger cannot do it. It is because modern 120v battery chargers use an auto-shutoff feature to just "give up" when the voltage fails to rise as quickly as the charger's electronics require. A solar panel with even a China made $20. protective Amazon.com charger will NOT give up, it will keep attempting to charge, until the target voltage is reached. When the battery comes down to a low voltage, the inverter will kick back on, and the cycle repeats. You can often use a solar inverter to output 12 or 24 volts when you set it up, useful for some heavy equipment like my 43k lb. Case excavator

I have had several instances where battery chargers faulted to the red indicator LED which is very frustrating. But not a problem with solar panel efforts. In my case I was using 216 watt Sharp panels, which can put out as much as 28 volts. The China inexpensive inverter will not feed the dead battery the 28vdc, only 13.8 to 14.1 (in my experience). I am not stating that you need as powerful a solar panel as mine, lessor wattage outputs will work too. I have only charged lead-acid batteries, as I have no Lithium or AGM type. China charging inverters from my experience are DOA, about 1 out of 10 is just non-funtionable.


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