Premade:
I found this USB boost pack that uses 18650 batteries (also I found quite a few 4 packs of 18650 batteries for around $8)
http://www.ebay.com/itm/300744677598" onclick="window.open(this.href);return false;
Basically it has USB port for charging cellphones etc, and a Mini USB port for charging the pack itself.
I think it is connecting the batteries in Parallel, so you could use just a single cell if you wanted. If the ebay item is sold, I used the search string 18650 USB (I always use price + shipping lowest first, and Buy-it-Now as options, if you want to see it this month check the US only button, but be prepared to pay 2x or 3x the price.)
Good:
- One thing to buy
Includes charger and protection
5v output
Battery meter
Flashlight
- Only 5v output
batteries are in Parallel (Maybe)
Only USB Mini charging
Case is large, PCB isn't easy to solder too
DIY Option:
If you want to DIY you can use a LM2596 regulator, $1.53 (maybe more than one if you need several voltages), this great thing can step down to any voltage you want, up to 30 or 40v!!. Input voltage must be higher than output, turn the little Potentiometer screw to set the output voltage.
Another bonus is dual voltages with only 1 regulator. The high pack voltage will allow you to run some parts of your project directly from the pack, 2 cells are good for near 7v, 3 cells for 12v, 4 cells for 15v.
LM2596 Regulator $1.53
http://www.ebay.com/itm/110950894139" onclick="window.open(this.href);return false;
Battery pack 2x - 4x $0.99 - $1.71
http://www.ebay.com/itm/140652926896" onclick="window.open(this.href);return false;
3x:
http://www.ebay.com/itm/290756182593" onclick="window.open(this.href);return false;
4x:
http://www.ebay.com/itm/150706506724" onclick="window.open(this.href);return false;
http://www.ebay.com/itm/390490690963" onclick="window.open(this.href);return false;
And you will need a charger, maybe two if you have more than 2 batteries $3 from China, $4 from USA
http://www.ebay.com/itm/280638594652" onclick="window.open(this.href);return false;
http://www.ebay.com/itm/330789765786" onclick="window.open(this.href);return false;
USA Charger:
http://www.ebay.com/itm/190687970923" onclick="window.open(this.href);return false;
Good:
- Choose your voltage
Higher Output
High pack voltage (2 cells: 6.6v-8.2v, 3 cells: 9.9v-13.2v, 4 cell:12.2v-16.8v)
Use a bunch of single cell holders to put the cells around the portable/project where they will fit.
- No protection as far as I know (you could add protection, OR use protected cells)
Separate Charger needed