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Recently I bought a 12V 200Ah battery for my solar system with 500W 18v (27A) solar panels. I find a label on the battery which is notice that the minimum charging current is 10% of the battery capacity. 10% of 200Ah is 20A.

Max. current comes from my solar panels in cloudy days is less than 10A,

So dose it means that the charging process totally stop in cloudy days or just become slow?

I want to connect two batteries together in parallel (400 Ah), so the minimum current to charge them become 40A? (according to this battery label).

Datasheet of battery.

enter image description here

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    \$\begingroup\$ Strange writing on the battery. I would no worry about charging it with a low current. But how do you terminate the charge? \$\endgroup\$ – winny Mar 5 at 7:34
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    \$\begingroup\$ This is the recommended current value of what is written on your photo above. The current less than 10% requires more time to charge. But it is admissible. A current of more than 25% of capacity can heat the battery, which leads to a decrease in service life .. \$\endgroup\$ – AltAir Mar 5 at 20:57
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Charging will certainly not stop if you charge with a smaller current, it will just be slower.

The reason to specify the minimum charge current is not entirely clear and not specified in the document you linked to. I can think of at least two possibilities:

  • This is the minimum current the battery is supposed to draw from a constant voltage charger, that is, a constant 13.8...14V source.

  • This is the recommended minimum charge current which prevents acid stratification after a deep discharge.

Unless you can find which one it is, I suggest to avoid the situation where your charge current is always below the minimum value, especially if the battery will rarely reach full charge.

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    \$\begingroup\$ It looks like a SLA, so it's almost guaranteed to be sulfation prevention. \$\endgroup\$ – yhyrcanus Mar 5 at 15:38

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