I use a Jackery external backup battery. It can fully recharge my HTC Thunderbolt up to three times before I need to recharge it. I keep it charged using a USB port on my PC when I am in the office and grab it when I am going to be on the road.
They sell larger models with much longer charges, but this one is about the size of a cigarette lighter and only costs $30.
20 posted on 04/22/2014 1:34:48 PM PDT by Bubba_Leroy
(The Obamanation Continues)