How to calculate the Watt Hours (Wh) of a lithium battery

If you intend to ship or you are traveling by air with lithium cells, batteries or battery packs, you will need to know their Watt-hour rating. This applies to lithium metal batteries (disposable) and lithium ion batteries (rechargeable).

Lithium-ion battery showing Watt-hour rating
Image 1: A Lithium-ion battery showing Watt-hour (Wh) rating on the case

This is usually stated on the battery itself (see Image 1). If not, you can calculate it as Volts x amp hours (Ah).

  • example 1: an 11.1 volt 4,400 mAh battery – first divide the mAh rating by 1,000 to get the Ah rating – 4,400/1,000 – 4.4ah. You can now calculate as – 4.4Ah x 11.1 volts = 48.8Wh
  • example 2: a 12 volt 50 Ah battery50 Ah x 12 volts = 600Wh

If you need it our Lithium battery watt hour calculator will work out your results for you.

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  1. Col Hodgson

    I have a 12V Lithium battery that has a claimed capacity of 42000 mAh.
    Yet the charge advice is 15V @ 2A for 7 to 8 hours.
    The discrepancy of battery capacity as 42 Ah (42000 mAh) and charge of 14 to 16 Ah is a puzzle.
    Battery capacity about 3 times the advised charging capacity?
    NB The Wh rating is given as 155 Wh that roughly equates to 14 Ah at an average of 11 Volts.
    Thanks for your assistance.

  2. Jeremy

    Just curious I’m trying to build a battery for my electric and it seems that it is comprised of 16 of the 3.7 volt 1-2-3 batteries. the battery casing claimed it to be 3.62 volt and 127.424 watt hours. So my question is does anybody know what a single 123 battery is rated at in terms of watt hours or amp hours?

  3. issac groh

    i have a lithium ion battery it comer with the WAHL DETAILER product i does not say any info on the battery besides that its 120v 60 hz, any idea what’s the wh of this battery ?

    Thank you


    I HAVE A MAX LITHIUM 21V 4.0ah BATTERY ON A LEAF BLOWER, CAN I USE A 21V MAX LITHIUM 7.5ah BATTERY ON SAME TOOL o want longer runtime it seems the 4.0 only last 15 to 20 minutes

    1. BatteryGuy

      That should be possible but we would always recommend you check with the manufacturer first.

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