2 cells in series are 7.4 volts - 3 cells in series are 11.1 volts

Then you gang them together in parallell to increase your Milliamps to give the safety and extended time for your motor.

For example:

3S-2P 1500MAH packs are 11.1 Volts and 3000MAH for longer flight times and to handle the motor draw.

The individual cells are rated for draw at a given "C" level. 1C being the pack's MAH rating. Some of the newer packs have as high as 12C. For Example the new Kokam 2000 MAH packs have a rating of 12 C. They are capable of handeling 30 Amps of continuous current draw. The Kokam 2100 Packs can pull as much as 42 Amps Continuous. Most on the market should be held at about 5 C to be on the safe side, unless they have a given maximum current.

My Multiplex 3S-1P 1500 packs have a warning on them to not exceed 12 Amps, at 5 C however they should not be ued at over 7-8 amps. (C rating Times MAH of cells divided by 1000) Check the "C" value of any packs you buy and be sure to put them in parallel if you have any doubt as to whether you will exceed their rating. You can parallel only batteries of the same MAH and for safety from the same manufacturer, and if you are lucky same lot number.

My Electrifly 720 3S-1P have no rating, but fly my Jr. Falcon drawing 8 Amps and do not even get warm after 12 minutes and more flight time.

And be sure that you always charge at the 1C rate for the pack.

Examples:

3S-1P 1500 MAH Pack is charged at no more than 1.5 Amps
3S-2P 1500 MAH Pack (3000 MAH Total) charge at no more than 3.0 Amps
3S-1P 720 MAH Pack is charged at no more than .72 amps
3S-1P 720 MAH Pack is charged at no more than 1.4 amps

All the above packs charge in about 1 hour to 1 hour and 10 minutes at these rates.

For charging I have purchased a Xantrex Power Pack 150. It has a built in Gel Cell and is designed as a replacement for jumper cables for your car. It allows you to plug your charger into a standard Cirar Lighter fixture. In addition it has an inverter allowing other functions. And in an emergency you can actually use it to jump start your car. Coleman also makes a similar device. It has been really useful. I use it in my shop for charging, as well as at the field. I always charge all my Li-Poly batteries before going to the field, and this device has enable me to fly a whole day without running down.