Power Capacity

         Power capacity is how much energy is stored in the battery. This power is often expressed in milliamp hours for small batteries. A milliamp hour is how much current (Amps) the battery can provide for some amount of time (generally in hours). This value the (Amps x hour) measurement is usually printed on the side of rechargeable batteries, expressed in mAh (1000mAh = 1Amp hour). For example, let’s say we have a battery with 1Amp-hour capacity, 1 Ah means that in theory we can draw 1 Amp of current for one hour, or 0.1A for 10 hours, or 0.01A (also known as 10 mA) for 100 hours.

However, the amount of current we can really draw (the power capability) from a battery is limited by the type of battery. For example, a coin cell that is rated for 1 Ah can't actually provide 1 Amp of current for an hour, in fact it can’t even provide 0.1 Amp without overextending itself. It’s like saying someone has the capability to travel up to 10 miles. Walking the distance is achievable but running 10 miles may not! Likewise, a 1Ah coin cell has no problem providing a 1mA for 1000 hours but if you try to draw 100mA from it, it'll last a lot less than 10 hours. So we come to the C rating.

C Rating

       So what does the C rating on a battery mean? The C in C Rating on Lipo and Life batteries stands for capacity. In its simplest terms, the C rating is the maximum safe continuous discharge rate of a pack. If you see 10C on your battery, it means it can be discharged at 10 times that pack's capacity. Capacity refers to the milliamp-hour rating of the battery, which as previously stated should be printed on the side of the battery. (2000mA for example).

Eg

             7.2 volt 2000mAh 10C

             2000 milliamps = 2 amps

             2 Amps x 10 = 20 amps continuous discharge

This means that you can safely draw up to 20 amps continuously without doing damage to your battery.

An 1100mAh LiFe battery has a 1C value of 1.1.

       Some battery chemistries give much fewer amp hours if you discharge them fast. This is called the Peukart effect. This has a big effect on alkaline, carbon zinc, zinc-air and lead acid batteries. For example if you draw at 1C on a lead acid battery you will only get half of the capacity that you would have if you had drawn at 0.05C. This effect is small in NiCad, Lithium Ion, Lithium Polymer, and NiMH batteries.

Because of this it is preferable to use NiMh over alkaline for driving winches and servos,

as the voltage of an alkaline will drop quickly under high discharge.

How Long will the battery last

       A rough guide for choosing the battery for your model. If you know or can measure the current

that the model will use (total of winch, motors and servos)

if you divide battery amp hour by model total amps it will give time of use.

If the model takes 500mA

2500 mAh /500 = 5 hours;

This is not accurate for many reasons and don't expect to get 5 hours but it will give you an

idea to work with