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A drop in capacity is normal because the battery crystals when it's not used too often
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The main reason why the battery is not satisfied is that the liquid on the panel is dry or vulcanized, which can also be charged slowly with a small current, and then charged to a multimeter, if the voltage rises, you can use the original charger to charge. You can also use two batteries for charging. Find a fully charged battery and put it in tandem. Then charge it. For example, two 12-volt strings become 24 volts, and it is time to use a 24-volt charger to charge him
A: Under normal circumstances, if the battery is good, the battery conversion light turns green and then charged for 2 hours to be full. If it can only be charged for 80%, it is not ruled out that the battery has been damaged. If you want to repair it, I think the first time to open the battery and add some steamed water, and the second time to find a charger with a smaller voltage than the normal charging charger. Activate the damaged part so that the battery can be fully charged later. Explanation completed.