When can I change a failed battery?

If it is determined that a battery has failed it is possible to change out that battery within the first year. After that it may be necessary to change out the entire battery pack. The batteries change chemistry over time and use. If you were to change only one battery, that battery could charge at a higher rate than the rest and could charge too rapidly and which could cause it to fail. It is best to simply disconnect the troublesome battery from the bank.