Listing capacity in Wh rather than MJ is fine, but many batteries are rated in amp-hours which isn't very helpful unless you also know the voltage. This is part

Listing capacity in Wh rather than MJ is fine, but many batteries are rated in amp-hours which isn't very helpful unless you also know the voltage. This is particularly annoying when it comes to "smart batteries" such as this USB power pack[0] where you have specs listing "10000 mAh" and "5 volts", but the actual capacity is around 37 Wh because they measured amp-hours at the internal battery and the battery voltage isn't exposed to the user. (Yes, the product description halfway down the page does say "10000mAh/3.7V" in small print if you know to go looking for it, but this isn't noted anywhere in the title or the "About this item" section at the top.) [0] Example: https://www.amazon.com/10000mAh-Portable-Charger-Stylish-Compact/dp/B08D9J2NJP/ https://www.amazon.com/10000mAh-Portable-Charger-Stylish-Com...