You have both batteries down at the same time and can't use either if they're both dead. Doesn't make sense to have a charger that will continue to keep one battery charged and fresh, while enjoying the other? Com'on Man! This is a no Brainer!\r\n
Answer - brownkibbe
If you look at accessories on their website, there is an external battery charger that you can purchase. Hope this helps!
Answer - pileperch
firefly does have an external charger that you can order. It will charge your dead battery while you are using the fresh one. It takes 45 minutes to charge