I have a Droid charger with a USB port to charge a 2nd... I have used it with no problems.
Is this a car charger or a mains charger?
I'm asking because I too have a Moto, and I've been very tempted to plug my eGo chargers (one normal 510-thread, 4.2V, 420mA, one passthrough) into the Motorola mains adapter, but it is labeled 850mA whereas the mains-USB adapter I got with my eGo kit is just 500mA.
So I'd be very very grateful if you could check what current your Droid charger supplies!
(To keep this a tiny bit on topic for this sub-forum: I so wish vendors would be more specific about the chargers they sell. Every now and then I read exhortations to not use eGo-chargers for smaller 510
batteries, but very seldom any actual specs, not to mention specifications for optimal current and voltage for charging. It is a bit annoying, I would love to get a universal charger with variable voltage and current output, but I would need to know what the recommended currents are for different batteries (I'm assuming anything = or < 5V should be fine). I've seen some site selling 510-chargers that only give 150mA, I can't believe that is the highest current even the smallest batteries will tolerate. Mine are still pretty new, but they seem to take the charge from the 420mA eGo charger just fine.)