Do you have an old battery pack from a laptop? If you are handy, you can cut it open and it may have several 3.7v LiIon batteries in it. Usually there is one bad one and the rest are good. They will usually be of the 18650 4000mAh 3.7V Rechargeable Li-ion Battery style.
http://www.ebay.com/itm/171259114562?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
When ordering on ebay, pay particular attention to the Estimated Delivery date. Always assume the later date of the range and you will seldom be disappointed.
When fully charged, they will read 4.1 volts. 3 in series will give you near abouts 12v. 4 Amp-hours is a respectable amount of juice.
John