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I have a solar panel that provides max 7V and average 5.5V under the sun. But it cannot produce enough current even for a little 3V DC motor. Can this solar panel charge a 3V battery? Or maybe two 3V batteries?

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  • \$\begingroup\$ Look at the specs of your rechargeable batteries and see what charging current they require. Similarly, check the specs of your solar panel and see what current it can provide. \$\endgroup\$
    – Nazar
    Jun 23 '14 at 13:05
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As long as the solar panel can provide an output voltage higher than the battery voltage, and current higher than the battery's rate of self-discharge, it'll charge the battery.

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  • \$\begingroup\$ Interesting concept there - battery self-discharge. I guess that was something I've never really considered before. Since something like an AA battery is claimed to last decades, this rate must be quite slow? \$\endgroup\$
    – sherrellbc
    Jun 23 '14 at 13:28
  • \$\begingroup\$ @sherrellbc A AA battery that is claimed to last decades would be an alkaline battery (i.e. non-rechargeable). Rechargeable batteries in general have a much more noticeable self-discharge rate. It is temp and SOC dependent. For Li-ion's it's 1.5-2% according to manufacturers: en.wikipedia.org/wiki/Lithium-ion_battery#Self-discharge \$\endgroup\$
    – horta
    Jun 23 '14 at 14:36
  • \$\begingroup\$ The Wikipedia "self-discharge" article implies that primary alkaline batteries typically have a shelf life of 5 years. The best (lowest) self-discharge rates in that article are 2% per month -- i.e., 22% per year. \$\endgroup\$
    – davidcary
    Jun 23 '14 at 18:11

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