How much time to charge 3000mah battery?

The milli-amp-hours rating has nothing to do with the voltage. The rating should be something like 3000 mah at 12V or 3000 mah at 1.5V.

One common 3000 mAh battery is 3.0 volts; another is 3.7 volts. A common camcorder battery is 7.4 volts. Some DeWalt tools use 12 V 3000 mAh batteries.