Batteries of the new age can't be allowed to get low on volts cos the chemistry inside them has a fight and burns the house down. So they cut themselves off once they get low. Think of an ego battery - once the charge gets low it still has plenty power to brightly flash the fire button and inform you it needs charged, but it won't supply any power out. The protection you refer to is similar ie it'll stop working when volts get low. Unprotected don't have this protection so you need to notice when the power is getting low and make sure you charge it before the house fire. Vamo's, as stated above, have built in protection so they'll stop working before your battery gets too low, and therefore unprotected are fine. There's also some reports of protected batteries not working in Vamos, something to do with the two protection circuits fighting against each other I believe.