You need connect it to a 9-15 DC volt source to charge batteries between 4 to 12 cells.
12Vdc 1A source is a bit low in current supply and may fully charge your batteries and the source need 1.4C.
Take a battery capacity of 1000mAh as an example:
1C: uses 1000mAh (1A) charge current to battery (the charge current is equal to the battery capacity).
It takes about an hour to be fully charged.
2C: uses 2000mAh (2A) charge current to battery (the charge current is 2 times of battery capacity).
It takes about half an hour to be fully charged.
1/2C: uses 500mAh (0.5A) charge current to battery (the charge current is half of battery capacity).
It takes about two hours to be fully charged.
According to these examples above, we can know that it takes about 20 minutes for 3C (3A) and 15 minutes for 4C (4A).
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