Take the Battery Mah rating, divide that by the Charger output, and that will give you the length of time.

Example-- Check the back of the wall plug for the charger. It will have an output rating (ex. output 500 Mah). If you have a 1500 Mah cell in your ignitor, take 1500 (Battery Mah), divide that by 500 (Charger output) and you get 3. That is how many hours to get a full charge. If a battery is NEW and being charged for the first time, you should let it charge for 10 hours, or overnight, to ensure a full charge.