USB DC-DC 3V to 5V 1A Adjustable Power Supply Boost Module

This unit will run on a single AA battery up to 3 AA batteries, C, or D cells... When I first tried using it I received the "Illegal Charger" message from several phones. After doing some research the Dand D+ pins need to be shorted together (little blob of solder between the two inside pins on the module does the trick) this tells the USB device that it is a Dedicated Charger Port (dumb wall charger for charging USB devices). The lower the input voltage the higher the current draw i.e. a single AA battery will work very hard and get extremely hot. I ultimately wound up using 3 C cell batteries in a 4 C cell battery box and mounted the boost module in where the fourth battery would go. With three C cells it can charge up an HTC smartphone to about 35 to 40% charge (about one hour) if the phone is turned off. After the blue LED goes out the unit is in scavenge mode and can draw as much as 3 amps out of the batteries (this makes AA batteries get really hot and split open thus the use of C cells). I would recommend changing the batteries when the blue LED goes out and it is still under load if you remove the load (unplug your phone) the blue LED goes out normally. So far I can charge a first generation NOOK, Blackberry Bold, Motorola DROID RAZR M (the very limit of this device's ability), and an HTC EVO 4g LTE (also the very limit).

Bottom line I recommend at least 3 batteries in series so your as close to 5 volts as possible and the unit doesn't work as hard also larger size batteries like C or D cells especially if your charging smartphones which are power hogs. If your going to charge iPhones or iPods I would recommend looking up the Mintyboost by Lady Ada as you will have to put 2.0 volts on the Dand D+ pins for the iDevices to charge properly and she has an excellent write up on it.