hi, i found a great article on WattFlyers forums, here the part that tell about Battery, realy intresting and well explaine:

AMPS vs. VOLTS vs. C

By Ed Anderson

aeajr on the forums

This brief discussion is intended to clear up a few terms and concepts

around electricity as it applies to electric airplanes.

Think of electricity like water. Volts = pressure Amps = flow

Volts is like pounds per square inch, psi. Says nothing about how much

water is flowing, just how hard it is being pushed. You can have 100 psi

with zero water flow.

Amps is flow, like gallons per hour. You can have flow at low pressure and

you can have flow at high pressure.

Amp hours is how much flow can be sustained for how long. It is used as a

way of measuring how much electricity is in the battery. Like how many

gallons of gas in your tank. It is a capacity number. Says nothing about

flow or pressure, it is about capacity.

Amps and mili amps? We are just moving the decimal point around.

1 amp (short for ampere) = 1000 miliamps (mili means 1/1000 amps)

Examples

So a 7 cell NIMH or NICD pack provides 8.4V (pressure).

The motor will draw electricity from the pack at a certain flow rate, or

amps.

If you have a 650 mili amp hour pack, it can deliver a flow of .650

amps (650 miliamps) for one hour. If you draw it out faster, it

doesn't last as long. So your motor might pull 6.5 amps for 1/10 of an

hour, or about 6 minutes.

A 1100 mah pack has double the capacity of the 650 mah pack, so it should

last "about" twice as long.

What is C in relation to batteries?

C ratings are simply a way of talking about charge and discharge rates for

batteries.

1C, = 1 time the rated mah capacity of the battery. So if you charge your

650 mah pack at 1C, you charge it a 650 miliamps, or .650 amps.

1C on a 1100 pack would be 1.1 amps.

2 C on your 1100 pack would be 2.2 amps

Motor batteries are often rated in Discharge C and charge C.

So a 1100 mah pack (1.1 amp hour) might be rated for 10C discharge, so you

can pull 11 amps ( flow ) without damaging the battery.

Then it might be rated at 2C charge rate (flow), so you charge it at 2.2

amps (2200 mah)

How did I do? Things clearing up?

If you have a 500 mah pack - any kind - and it is rated at 16C that means it

can deliver 8 amps.

If you have a 1000 mah pack - any kind - and it is rated at 8C that means it

can deliver 8 amps.

If you have a 1000 mah pack - any kind - and it is rated at 12C that means

it can deliver 12 amps

If you have a 1500 mah pack - any kind - and it is rate at 8C that means it

can deliver 12 amps

If you have a 1500 mah pack - any kind - and it is rated at 20 C that means

it can deliver 30 amps.

If you have a 3000 mah pack - any kind - and it is rated at 10 C that means

it can deliver 30 amps.

So, if you need 12 amps you can use a pack with a higher C rating or a pack

with a higher mah rating to get to needed amp delivery level.

One last point. Motor batteries vs. receiver batteries

Some batteries can sustain high discharge rates. Others can not.

Those used as transmitter/receiver packs typically are made for low flow/amp

rates while those made for motor packs can sustain higher rates.

Having a 600 mah pack does not tell you if it is a motor pack that can put

out 6 amps, or if it is a transmitter/receiver pack that would be damaged if

you tried to pull power at 6 amps. It is enough to say that they are

different.

Clearly a motor pack could be used for a transmitter/receiver job, but a

transmitter/receiver pack should not generally be used as a motor pack.

It is best to size your battery packs so they run somewhat below their

maximum C rating. You will stress them less and they will last longer. For

example, if your motor needs a pack that can deliver 10 amps, getting a 1000

mah pack that is rated for 10C ( 10 amps ) will meet the spec, but it is

running at its limit. A 15 C rated 1000 mah pack would be better, or

perhaps a 1300 mah 10 C pack. In either of these cases, the pack will be

less stressed and should handle the load much better over the long term.

Other Resources

Basics:

http://www.modelaircraft.org/mag/FTGU/Part8/index.htmlLithium Batteries

http://www.rchobbies.org/lithium_batter ... hrough.htmLithium Balancers and Balancing Chargers

http://www.rcgroups.com/forums/showthread.php?t=599287New Electric Flyer FAQs

http://www.ezonemag.com/pages/faq/a105.shtmlA series of posts on electric power system basics

http://www.wattflyer.com/forums/showthread.php?t=1933http://www.rcgroups.com/forums/showthread.php?t=417868MotoCalc

MotoCalc will tell you everything you need to know: Amps, Volts, Watts, RPM,

Thrust, Rate of Climb, and much more! It is a popular tool for predicting

the proper motor, prop, battery pack for electric planes.

http://www.motocalc.com/Electric Motors Described

http://adamone.rchomepage.com/guide5.htm