The first charger takes a higher voltage and cuts the voltage down producing heat, in other words wastes energy, and as the batteries or source are put in use, the battery power beings to decrease to the point where the batteries can not power up five volts which causes you to switch batteries. But the batteries still have power in, just not enough to power your device so DON'T THROW YOUR BATTERIES AWAY.
The second charger I believe is a more efficient design such as a MINTYBOOST . It takes a lower voltage and it bumps it up to the voltage needed thus not wasting as much power. The only drawback is that you are now stuck with a shorter lifespan, which for some isn't bad, but I like the life span and the efficiency.
Here I will make a 4 AA battery charger using the "AnyVolt Micro" from Dimension Engineering. It will bump the voltage down while batteries are fully charged and then when the batteries reach a much lower voltage say half power it will switch automatically to bump the power up to a desired voltage. Thus using your batteries thoroughly.
While writing this I have run across another marvel from Dimension Engineering called the LVBoost. This device will run the batteries lower thus making your device run longer. BUT the device only goes to a max 5volts at 1 Amp so this will only work for devices that can operate at 5 volts, which would actually work for this project with a smaller battery pack. I wanted to make something that I could use 4 AAs or higher and be able to power something up to 14 volts.
There is also some minimal SOLDERING for newbie's!!!!
Step 1: Materials
1 - USB Female Connector preferably one already wired and neat so you can put it in your favorite project case. (I used one that came with my motherboard) - $Free or cheap $3 USB extender
1 - AnyVolt Micro - $20-25 (the most expensive part but you'll make it up with those expensive AA's ur gonna be getting through time.)
1 - 4 AA Pack with batteries (built in On/ Off not required, but I figured I make sure that im saving power) - $4-5
1 - 10k Resistor - $pennies
Soldering Iron - $(should have one otherwise this may be the most expensive part)
Any Shrink Tubing if you choice - $again pennies
Step 2: Take It OFF!!! and Put It Back On....
Strip the wiring on your battery pack revealing the Black and a RED wire.
Solder the Red from you battery pack to the Vin port on the AnyVolt.
Then the Black to the GND port. You may want to put the Black wire form the USB connector here as well.
Now finally the RED wire from the USB should go to the Vout port on the AnyVolt wire to the Voltage Out on you AnyVolt.
Step 3: TEST
Step 4: IPhone Support
I'm not an expert but I'm a little stupid, I just touched the green and white cables and it actually worked. The Itouch went into charging mode.
Now i just wanted to be safe so i bumped the 1.2 volts down with the 10k resistor and it worked just fine.
Step 5: Ain't It Puuurrrty....
Step 6: All This for Just This?!?
This means you can power any device just by tuning the Voltage to the device specifications. By the way, you might have to change the connector on the end by utilizing that black and red wire again.
I also put a picture of the device with nothing changed running off 2 Batteires showing it will go down to 3v and lower. The 2 red wires are there to complete the connection so it will work.
CONGRADULATIONS!!! you have now made a USB charger that is more efficient and longer lasting than most if not all commercial portable USB chargers!