4 rechargeable AA batteries to standard USB power line

[blek]

basically, i bought this $5 worth of battery holder that is supposed to connect to USB to power some of my devices (basically, a backup source). i already have 4, 3800 mAh AA Ni-MH batteries (or so the label says), so i was like cool.

but the thing is the battery holder doesn't really work. so it laid in a tiny box in my room for almost 2 years. now that i'm re-organizing my stuff i found it again. i opened it and no surprise, it doesn't have any regulator of sorts. it just connects the batteries in series.

i know, i could just get these:
http://www.ebay.com/itm/4-AA-Battery-Holder-Box-Case-1PCS-4-8-5-9V-DC-USB-OUTPUT-Switch-Buckle-/160673519843
nowadays for almost the same price. (albeit it doesn't seem to be able to regulate a constant 5V @ 1A like standard USB does)

i have a lot of electronic parts that i've scavenged, so i thought it's a good idea to finally put some of them to use.

i  figured it needs a stabilized switching regulator to do this, and it would have to be tiny and efficient... any ideas for a schematics, guys?

 

[blek]

also have a couple of 115-220V AC plug to USB power adapters to spare. maybe i could rip a few components from those?

honestly, i know very, very little about electricity/electronics, and i can't deny it.

 

[Hero999]

You need a voltage regulator to convert the 4V to 6V from the batteries to a stable 5V supply for the USB devices.

I seriously doubt the batteries you've bought are really 3800mAh, they're probably more like 1000mAh.

 

[audioguru2]

For many years, AA Ni-MH rechargeable battery cells had a capacity of 2500mAh, but they self-discharged in 1 month.

In the past 6 years new AA Ni-MH cells have a capacity of 2000mAh to 2300mAh and hold their charge for 1 to 3 years (Sanyo Eneloop).

Sony claimed a very high capacity of  3800mAh a few years ago which was probably an error. Now they sell 1000mAh AA Ni-MH cells.

 

[Hero999]

My advice would be to use six batteries in series and a switch mode buck regulator to reduce the voltage to 5V. If you don't have room for more batteries then use AAA cells instead but bear in mind the capacity will be lower.

A SEPIC converter can generate 5V from 4V to 6V but it's a bit harder to make than a buck regulator for which there are many ICs available.