How long does it take to charge a flip camera fully?

The quoted figures for the Flip Ultra HD are - up to 2.5 hours battery life and a 6 hour recharge time via USB.

Different Flip cameras have different batteries. If your Flip has AA batteries these can be replaced with fresh ones while the old ones are recharged in a battery charger which will probably take six hours/over night. Some models have a built in battery and others a rechargeable battery pack which can be replaced by AA batteries if required.