What is C Rating on LiPo Battery

C rating is one of the most important factors to consider when buying LiPo batteries. In this tutorial we will explain what C rating is and how it’s calculated.

Make sure to check out our tutorial about mini quad LiPo batteries.

LiPo Battery C Rating Explained

C Rating is an indicator of the continuous discharge rate of a LiPo. It allows users to easily calculate the maximum constant current you can draw from the LiPo pack safely without harming the battery.

Max Current Draw = Capacity x C-Rating

For example, if you have a 3S 1000mah 20C LiPo pack, your safe max current draw would be 1000ma x 20C = 20A.

You might wonder, can I draw more current than the above figure (i.e. over the 20A given in the example)?

You could, but it’s not recommended.

Discharging a battery too quickly is bad for the health of the battery. It will raise the internal resistance faster than discharging within the battery’s limit.

Internal Resistance

To explain these issues, we need to understand what internal resistance (IR) is. Every LiPo cell has internal resistance, and this is what limits the max current draw of a LiPo battery.

Ohm’s Law: Voltage (V) = Current (I) x Resistance (R)

Energy that is lost to resistance will turn into heat, and this is what causes the battery to get warm when discharging at high current. The pack can even become swollen (or “puff”) in extreme cases.

Since the formula V=I*R is constant, to maintain the desired current, the voltage required is proportional to resistance. That means if you have a high IR in your battery, you will suffer from bad voltage sag when using the throttle aggressively. When the voltage of your battery drops, your motor will lose RPM and the aircraft will lack “punch”.

Note that IR will increase as the battery gets older, but it can be affected by other factors too, like a change in temperature (why battery performs worse in the cold winter?)

Also note that some battery packs have low IR, probably because of the high C-rating, but it’s not always true that high C-Rating batteries necessarily have low IR.

Can You Trust C Rating?

C rating can be a useful tool to help you select a LiPo pack, unfortunately many RC LiPo manufacturers nowadays overstate C-rating values for marketing purposes. Therefore, while C rating is an indication of how good a LiPo is, it’s not everything.

The best thing to do is to find out about a battery’s true overall performance by looking at third party testing and reviews.

Remember that cheap batteries are usually inferior quality, which means IR will rise quickly, and voltage sag will become more and more pronounced, negatively impacting the lifespan of the battery.

Edit History

  • Feb 2015 – Article Created
  • Jan 2018 – Updated

38 thoughts on “What is C Rating on LiPo Battery

    1. Oscar Post author

      In theory, higher C rating gives you higher max discharge current while it increases the battery weight and cost.

      Reply
  1. Kostas

    Hi Oscar.
    I found your articles very usefull.
    I am building a fishing boat (5-6 kilos with the batteries) the motor that i am going to use is the xerun 4274sd 1800kv 1300watts and i am intending to use 4s 10000mah baterries.2 of them
    I want to ask you which c rating should my baterries have for economical use.I dont want to drive it fast only for fishing
    Thanx a loy

    Reply
    1. Oscar Post author

      We wouldn’t know until you have the motor tested in the water with propeller on. I have no previous experience with RC boats.

      Reply
  2. Jim D.

    Hey Oscar!
    Great info for us rookies! Thanks for that!
    I definitely understand more having read a couple of these posts from you!
    A friend and I started with some Aeris Shadows (To get a Cheap feel for flying) and are currently building our own using:
    A Realacc Phoenix frame
    Racerstar 2205 (2300kv-friend, 2600kv-myself) motors
    Dal Cyclones t5045 props
    30a v2 x4 ESC’s
    Evo F3 FC
    Plus a few other bits
    We’re planning on running Runcam Owls, probably 2plus’..
    My/Our question is, what size would you recommend for us? We’re considering 2200mah 65c’s for the obvious advantage of MORE POWER!! but we understand our drones may not be beefy enough..
    Thanks again!
    Jim D

    Reply
    1. Oscar Post author

      I think 1300mah – 1600mah is the best size for your quad. 2200 is way too heavy you will lose a lot of agility over that :)

      Reply
  3. Wasantha Weerawarna

    Hi Oscar,

    Very nice article. Could you clarify bit more of whatvyou said to choose the correct battery for me pls.

    Hexacopter with DJI Naza M V2.

    Motors – 4114 400kv 4-8s motors (max current draw is 25.6A) Max Thrust is 2980g
    ESC: hobbywing 40A 6s Opto. This is only recommendation I found that is compatible with Naza M V2.
    I have a Multistar 5200mAH 10C battery.

    And with the given calculations, is not good enough? If not what would be the best battery in terms of discharge rate?

    I prefer to buy another of the above battery and add more flight time if I can use it. Can you pls advice? Since ESC supports only 6s is this possible? I mean coupling the two batteries? Or do you advice me to buy a 6s high capacity battery with higher C rating?

    Expect a favourable response.

    Cheers

    WAS

    Reply
    1. Oscar Post author

      according to your information, the max current draw that can happen in your setup is about 150A.
      5200mah 10C in theory can only supply 52A max continuously, or 104A at burst (burst C rating is usually double of the continuous rating, but double check and confirm with your battery)
      So it’s not quite enough IMO, I would probably get something higher than 20C, that should give you 100A+ current and 200A at burst, given you might use 100% throttle during flight, and it doesn’t happen longer than 10 seconds.

      Reply
  4. James V

    Hi Oscar,

    It’d be helpful to know exactly how much power a cell would lose under a certain load.
    Is it possible to calculate the voltage drop or internal resistance of a cell from the C rating and capacity?

    Thanks.

    Reply
  5. Ashvini Kumar Sharma

    Hello Oscar , I am using A2212/13T motor which have a max current rating is 13A, I am building a quadcopter , I bought 30 A ESC and 3600mAh 25C lipo battery ? Is this a good choice because my quad is not lifting up one motor runs faster than the other three, please help me

    Reply
    1. Echo246

      Hi,
      Try calibrating your ESCs if you are using an analogue protocol (i.e oneshot 125 or multishot)

      Reply
  6. Aliff Nuriman

    Hi Oscar,I need help.Im about to choose LiPo battery,i calculated my maximum current draw on 100% is 58A.If i choose LiPo that is calculated (4A*15C)=60A.Is that okay if choose that?

    Reply
  7. ponnex

    I have DYS 1306 3100KV motor in which its draws around 8A to 10A based on specification. It’s safe for me to assume that my set up will draw max of 40A only(10A per motor x 4)? And I can make it to 45C LiPo giving an extra window? As well as I can assume that having a 65C LiPo will be the same with 45C since I wont be drawing close up to 65C?

    This question relates to LiPo weight and total efficiency.

    Reply
    1. Oscar Post author

      it depends on the props, if you are using the same props in the data sheet then yes you can assume the max current draw is 40A. Having higher C rating battery doesn’t hurt.

      Reply
  8. jordan

    hi
    I have just purchased a quadcopter and the battery is 3.7v 600mah however is does not tell me the c rating. I have just got 4 new batteries, they are all 3.7 600mah but have 25c on them. Now they do not last as long as the original battery so does this mean that the original battery has a higher c rating?

    Reply
    1. Oscar Post author

      could be, when max continuous discharge current is below your usage, the voltage will drop more dramatically, and thus giving you shorter flight time.

      Reply
  9. Adam Wechsler

    So then what’s the difference between a 3000 mAh 20C battery and a 2000 mAh 30C battery? Both would have a max current draw of 60 A.

    Reply
  10. 3badi

    Hi, Oscar!
    Can you help me, please?
    It’s my first time to build my homemade boat running with:
    HobbyKing 60A ESC
    Brushless 3100KV Motor, Max Amps: 56/38A
    11.1 V 5200 mAh 10C

    after 5min of my first test, the battery has gone Overheating.
    what is the best battery to using for my boat?
    what about if I connect tow batteries in parallel?

    regards,

    Reply
    1. Oscar Post author

      I think you are getting too close or even over the max current output on the battery.
      To increase that, you can either up your total capacity or battery C rating.
      So yes you can try putting another pack in parallel that way can up your total capacity.
      or get some higher C rating battery (given it’s same capacity or higher capacity)

      Reply
  11. imran

    Hi Oscar

    My name is imran

    It s my first time to build my zmr250 quad
    Dys 1806 2300kv
    Afro 12 a ESC
    Naze 32
    Marek pdb

    But i don’t know which battery and how much c count to buy

    Reply
  12. Mehul Mahajan

    Hi Oscar,
    We have ordered a dys 3S 25C 2200 mah battery for our quadcopter but we dont know how much will be the flight time. can u please tell me the flight time of this battery. If u know any other battery which we can use plz tell me???

    Reply
  13. DoFPV

    hello oscar… need advice

    currently wait for shipment arf all rcx frame h250, rcx motor (not yet know the spec), esc blheli 20A

    currently awaiting shipment my arf quad race arf rcx h250, rcx motor (not yet know the spec), esc blheli 20A, a friend offered me Dinogy 4S battery 14.8V 2250mAh 65C. is it proper ?

    Reply
    1. Oscar Post author

      it should fly, but I think it’s a bit on the heavy side… i would prefer 1300mah to 1800mah..

      Reply
  14. collin

    Hi Oscar
    I’m not sure exactly how this correlates to my motors/escs. If I have six 20 amp escs at 11.1V what C rating do I need?

    Reply
    1. Oscar Post author

      Hi Collin
      You can work out the max current draw of your motor and propeller combination. Let’s say your motor/prop combo draws 17A current at 100% throttle for example, then your quadcopter can draw 17*4=68A max.
      in that case, battery C rating = Max current / Battery capacity.

      of course this is only theory, you can use lower C rating batteries within reasonable range.

      Reply
  15. Andrejs

    Hi, Oscar!
    Can you help me please?
    I will have two 250quads with 1) Sunnysky X2207S KV2100 and 2) Sunnysky X2204 2300KV.
    What battery I need to buy for both?

    Reply
      1. Andrejs

        Thank you for your answer! :)
        Yes, I want to buy 4S battery. But if I will by 2200mah? How much C i will need? 45-90C will be fine? Or 65-130C will be better?

      2. Andrejs

        Big thanks for your answer and also for your helpful information in a blog! Have a good day! :)

  16. Cogur

    Hi Oscar,

    First of all thanks for the work you done to make the RC community easier.

    I’m about tho build a 250 sized quadcopter
    zmr250 carbonglass and DYS be1806 motors.
    the max amp of the motors are 31a

    I’m about to select the perfect battery for this build. I’m realy a beginer in the RC world and i would like to select a battery with which I can have long fly time. For now the agility is not that important.

    Based on your articles I would need a battery with 35+ C rating to be able to handle additional stuffs with it later. and based on others comment Its recommended to use a 3s battery and It’s not recommended to use batterys largen than 2000Mah for a 250 sized quadcopter.

    So I decided to by something like this:
    hobbyking.com/hobbyking/store/__9937__ZIPPY_Flightmax_1800mAh_3S1P_40C.html
    or that:
    hobbyking.com/hobbyking/store/__11908__Turnigy_nano_tech_1800mah_3S_25_50C_Lipo_Pack.html

    But I’m not sure what is the 20-50C rating means? It can discharge with 20 to save the battry life and with 50 if it’s necesarry?

    Are those two batteries good choices for my purpose?

    Thanks for the response.

    Reply
    1. Oscar Post author

      HI Cogur,
      that’s right, you don’t get much benefit from heavy battery. 1300mah to 1800mah is a good range for mini quad.
      20-50C basically means 20C contant, 50C burst (max).
      Both of them should be fine for your setup :)

      Reply

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