Guidelines For Choosing A Lipo Battery

Choosing the correct Lipo battery for your model involves many factors, and you must first have an idea of the voltage and amp requirements of the motor/prop combination that you intend to use. For help in choosing the correct Motor, Propeller, and Electronic Speed Control for your model,  please visit my other information pages. For general information about Lipo batteries, please go to the Lipo Battery FAQ page.

The prop data section of the motor listings will help you determine whether to use a 2, 3 or 4 cell Lipo, and will provide you with the amp draw requirement of the motor and propeller that you choose. You should always use a Lipo battery that has an amp rating that is higher than what the motor/prop combination requires. For example, if the motor/prop combination requires 10 amps, you will need a Lipo battery that is rated for more than 10 amps. Lipo batteries last longer if they are not used near their maximum rating, so it is a good idea to use a Lipo that is rated for an amp output that is quite a bit higher than what the motor/prop requires. A good rule of thumb is to use a Lipo that is rated for about a 50% higher amp output than the motor/prop requires. So if the motor/prop combination draws 10 amps, then the Lipo should be rated for 15 amps or more. This gives you a nice comfortable margin between amps available and amps required, and the Lipo battery will not be stressed.

Here is an example of choosing a correct Lipo battery:    Let's say you want near vertical performance from your GWS Corsair, so you choose the 2410-12D motor and GWS 9050 prop. The prop data provided with the motor indicates that this combination produces a maximum 23 ounces of thrust at 12 amps when using a 3 cell Lipo battery. You want to choose a 3 cell Lipo battery rated for about 50% more amps than required, so......12 amps times 50% is 6 amps. Add 12 amps and 6 amps and the result is 18 amps. This indicates that you should choose a Lipo that is rated for about 18 amps, or more. Some Lipo battery choices would be an 11.1v 1200 15C (rated for 18 amps), an 11.1v 1650 20C (rated for 33 amps), an 11.1v 1800 20C (rated for 36 amps), or an 11.1v 2250 20C Lipo (rated for 45 amps). Which should you choose for the Corsair? Well, in this case, it's a simple process of elimination. The 11.1v 2250 20C is too long to fit in the Corsair easily, and it makes for a pretty heavy wing loading and high landing speeds. The 11.1v 1800 20C seems well suited for this size model, but the 4 inch length could be a problem. The 11.1v 1650 20C might be a very good choice, but you would want to see if a 3.5 inch long battery could be made to fit. Finally, the 11.1v 1200 15C seems to meet the requirements quite well. It's the lightest of the four batteries that we are considering, and also the smallest. And in fact, I know from using this combination that the 2410-12D, 20A ESC, GWS 9050 prop, and the WOW-RC 11.1v 1200 15C Lipo works very well on the GWS Corsair. Choosing a battery often comes down to selecting the lightest and most compact Lipo that provides the required amps. However, there is one more point to consider:  Lipos with higher amp ratings deliver more energy to the motor. So with our GWS Corsair example, you will end up with a little better performance by choosing the 11.1v 1650 20C (33 amp) Lipo over the 11.1v 1200 15C (18 amp) Lipo. The trade off is a little heavier plane. Some people prefer the lightest possible flying weight - others prefer increased performance.

Now, let's say you try to use a Lipo that is not rated for a high enough amp output.  If you use an 11.1v 1000 10C (10 amp) Lipo with the 2410-12D/GWS9050 motor/prop combination, the battery simply cannot supply the 12 amps that the motor/prop is 'asking for' at full throttle, and the battery is pulled down to 9 volts, where the ESC reduces power to the motor, or shuts the motor off completely, depending on what type of motor cut-off the ESC is programmed for. If the battery happens to be 'strong enough' not to sag to 9 volts, the high amp draw of the 2410-12D motor and 9050 prop will cause the battery to overheat, and the battery will very likely be damaged.

Some additional comments:  The amp draw data provided for the various motor/prop combinations are maximums. That is, the motor is stationary and running at wide open throttle on a test stand. During level flight with a model, the amp draw drops somewhat, even at wide open throttle. How much depends on the amount of drag and the pitch of the prop. Also, a lot of RC flying is done at lower throttle settings, resulting in a much lower amp draw than the maximum indicated from the test stand. I bring this up because there are times when lower amp rated Lipos, which are usually smaller and lighter, can be used simply because the motor/prop combination is not being used anywhere near it's maximum rating. For example, if the motor/prop combination draws 10 amps at maximum, but you know you will be running at half throttle most of the time, then the actual amp draw for most of the flight might be only 5 or 6 amps. In this case, it would be acceptable to use a lipo rated for only about 10 amps, if you feel it's desireable to use the lightest possible lipo.

One more thing. Excessive heat shortens the lifespan of Lipo batteries. If your Lipo battery is hot after a flight, you should consider using a Lipo with a higher amp rating, or fly the model at lower throttle settings. It's also best to have plenty of airflow over the battery if possible.