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Thread: mAh or C. Which is more important?

  1. mAh or C. Which is more important?

    Hello, given two batteries: Battery A has more mAh (e.g. 2000) than Battery B. However, its C value is lower. The mAh*C values are almost the same. Which battery do you recommend and why? Thanks.

  2. #2
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    Re: mAh or C. Which is more important?

    mAh tells you the capacity of the battery and the C rating or continuous discharge rating tells you how much current the battery will be able to supply to your project.
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  3. #3

    Re: mAh or C. Which is more important?

    If the C rating of battery A is good enough for your application, then the higher capacity is going to give you more runtime.

    However, I would expect battery A to weigh more, which may or may not be a consideration for you.

  4. Re: mAh or C. Which is more important?

    Thank you. How can I tell if the C rating is good enough or not? I recall somebody mentioning that it is better to get a battery with higher mAh*C value. Is that right?

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    Re: mAh or C. Which is more important?

    It depends on how much current you need. Like jwatte said, batt A will give you longer runtime since it has more energy. But if weight is important batt B might be a better choice. In general it's better to have a battery that can deliver more current.
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  6. #6

    Re: mAh or C. Which is more important?

    If I recall, 1C is the milliamps that the battery can put out in 1 hour. For example, if you had a 1000mAh battery then 1C is 1000mA or 1 amp. If you had a 2000mAh battery then the same 1C rating would provide 2 amps of continuous current. The C rating by itself is meaningless without also factoring in the mAh rating.

    You need to determine how many amps your project needs at max load and then get a battery that has at C rating that will provide at least that much power. As long as the C rating is high enough, going for a C rating higher than you need doesn't give you anything extra. When choosing a battery, I usually determine how much current I need then then find the largest battery based on mAh that will fit in the available space.

  7. #7

    Re: mAh or C. Which is more important?

    How can I tell if the C rating is good enough or not?
    How long do you need to run? Rate the battery for enough mAh that it can sustain the average current for at least that long.

    How much current will your motors/servos/controllers/equipment draw? On average? At peak?
    Rate the battery so that the C rating times mAh capacity divided by 1 hour is at least twice the average draw, and higher than the peak draw.

    Now, you probably realize that the battery is too heavy, so you have to compromise on runtime, and re-do the math (to reduce weight, lower the mAh, increase the C to compensate for draw.)

    For most robots, 10 C is a fine rating, and most hobby/RC batteries you get these days are more than that anyway. High C ratings are mainly for very high peak draw applications, like big brushless motors in RC cars, or quadcopter fliers.

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    Re: mAh or C. Which is more important?

    Quick example: HS Walker ran on a 20C 2200mAh battery, and only killed it because of being left on

    However, my twin engine RC aircraft requires at minimum a 2200mAh 30C LiPoly (2.2Ah X 30C= 66A continuous draw)
    The twin runs 30A power packs (motor+ESC) the 5000mAh I put in it is just bonus cap so I can fly for more than 7-10 min at a time.


    The batt for HS Walker only cost me $20. (Will give link if asked)

  9. Re: mAh or C. Which is more important?

    Thanks for the replies. I have two confusions. First, should I choose a battery with higher mAh or higher mAh*C. From this thread, it seems that mAH is more important especially when C is over 20. Am I right? Second, in the past, I read that higher C batteries mean they run out quickly due to larger discharge rate. So, this is incorrect?
    Last edited by Snoopy; 08-08-2015 at 10:00 PM.

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    Re: mAh or C. Which is more important?

    No, two batteries with the same mAh but different C will run out at the same time under the same discharge current. The only difference is that the one with higher C can deliver even more current. Still they will have the same amount of energy (wattage).
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