# Is there a way to estimate battery discharge duration from mAh and C-rating?

Lots of batteries are out on the web, and I understand what the values mean. But I would like to get a battery with a good discharge duration, so is there a way to tell an approximate battery life based on mAh and C-rating?

• Do you mean like how many charge/discharge cycles the battery can take before degrading too far?
– ifconfig
Oct 8 '20 at 19:39
• @ifconfig, that would be helpful, but no. I would like to know how long I can use the battery before I have to charge it. Oct 8 '20 at 19:40

The capacity and C-rating don't tell you how long the battery will last, just how quickly you could discharge it if you really wanted to do it as fast as possible.

It's perhaps analogous to the top speed of a car - just because your car can reach 120mph doesn't mean that a journey of 120miles will take an hour. Most of the time you'll never reach that top speed.

A high C rating is like having a really big fuel hose on a car. You might need it on a dragster but it won't make an ordinary car any faster, or use fuel any faster.

• "Most of the time you'll never reach that top speed, but a car with a higher" It looks like maybe you didn't finish what you were saying?
– Jacob B
Oct 9 '20 at 12:29
• @JacobB - thanks, I've clean it up a bit. Oct 9 '20 at 13:56

If you know the current draw of your aircraft - which you can either calculate by adding each component’s current requirement, or measure with an ammeter - you can estimate the flight time for a given mAh rating with the following formula:

$$Endurance = \frac{ 0.8 * Ah }{ AverageAmpsDraw } * 60$$ [source]

Note - if your battery is labelled in mAh, divide by 1000 for Ah

You may also like to take a look at this question, which is on a similar subject so might help (I have reposted part of my answer here, but I think that part of the answer was an aside to the question asked there...)

• I don't think you quoted that right. I believe it should be Ah in the numerator, not mAh if you're dividing by amps and not milliamps.
– ifconfig
Oct 8 '20 at 21:55
• @ifconfig You're right; I've fixed it. Oct 9 '20 at 6:58