How long does it take to charge an 8.4v 3000mAh NiMH battery?

It takes 9 hours 10 minutes to fully charge. Sometimes the wait will be longer, sometimes shorter. If you just used a battery for a short time, than it won't last 9 hours to charge. If you used the battery fully than 9 hours is the time it will take to charge completely. Every battery is different, and some may take longer.