"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!
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
If you look at accessories on their website, there is an external battery charger that you can purchase. Hope this helps!