How long does a LiPo battery last?

Other Hardware General Electronics
1

If I have a Lipo battery that has a capacity of 2,000mAh, does that mean that it outputs 2,000 mA per hour? So if I have a project that draws 400mA, to calculate how long the project will last on that battery, I would divide 2,000 / 400, which means that the battery will last 5 hours with that project?

Thanks!

2

Yes, except that its amps times hours, not per hour. Think about the units:

2000mAh / 5h = 400mA

If it were 2000ma/h, then dividing the capacity by time wouldn't make sense:

2000mA/h / 5h = 400mA/h/h

Capacity is simply electric charge, but often measured in Ah rather than C,
1Ah = 3600C

You can think of C (coulomb) as one As (amp-second).

3

Thanks! I think I'm still a bit confused though :frowning:

With a 2,000mAh battery fully charged, and an Arduino project that's drawing 400mA, how long will it last?

Thanks!

4

Awesome. Thank you!!!

5

osmosis311:
if I have a project that draws 400mA, to calculate how long the project will last on that battery, I would divide 2,000 / 400, which means that the battery will last 5 hours with that project?

Yep.

But don't depend on it. Battery life claims need to be taken with as much salt as car mileage claims.

6

Also keep in mind, most batteries are rated by finding the current draw that will last 10 hours, then multiplying it by 10. But if you draw current out faster, they lose efficiency. So a 2000mAh battery may last 10 hours with 200mA draw, but only last 45 minutes if you draw 2A.

Also keep in mind - your Arduino may draw 400mA. But if you are using a single LiIon cell and a voltage boost switch mode converter, in addition to the inefficiency of the converter, it must draw more than 400mA from the battery in order to turn about 4V into 5V@400mA. IE, 2W out means something more than 2W in. Say 90% efficiency, so 2.2W in, 2.2W/4V = 550mA. As the battery voltage drops, the current draw increases.

7

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8

You also don't want to drain a LiPo battery to anything less than 80%, after that you start damaging the battery

9

Perhaps you meant 40%?

Or did you mean, don't drain more than 80% of the capacity, IE, don't discharge below 20% charge?

10

Sorry, yes, don't use more than 80% capacity or to less than 20% charge. Typically that's around 3.2 volts but it depends on the exact cell, some will happily go down to 3v