How to compare Wh of various batteries?

I wanted to get myself a bit more familiar with how different batteries stack up (18650 Li-ion vs AAA NiMH) against each other in terms of total capacity & capacity for size/weight but realized I'm a bit fuzzy on the numbers.

I know Amps * Volts = Watts, so I'm assuming that Amp Hours * Volts = Watt hours/Wh? Is this correct?

I've got a Eagletac battery sitting in front of me that says 3500mAh & 13Wh on the packaging; So that is just 3.5Ah*3.7V correct? If so, I was just wondering why 3.7volts vs 4.2Volts?

Looking at Energizer's spec sheet for their AAA pre-charged NiMH it's rated .7Ah. To get Wh do I multiply that by 1.5Volts or Nominal 1.2Volts? If 1.2 that would be .84Wh. Are there other factors that significantly change the bottom line Wh?


I was also curious how different batteries compare in total capacity for their size and weight. For example the 2 batteries I've already mentioned:

Energizer AAA pre-charged lists - 11 grams and 3.8cm cubed. For my Eagletac 18650 I'm just roughly guessing the volume at 16.5cm cubed (I didn't measure - just assumed 18mm diameter/.9cm radius and 6.5mm length or .9 squared*3.14*6.5) and I did weigh it and found it to be 49 grams. So does this chart look right to compare Wh for size/weight?



So roughly could I conclude in this case the 18650 Li-ion has 3.8x as much capacity for it's size and 3.4x as much capacity for its weight?

Are there any charts out there already that compare this kind of info? I couldn't find Energizers numbers for Wh or Eagletac's for volume/weight...

Parametrek got you covered.

For Alkaline batteries the energy varies significantly with load current.
You best way to get comparable Wh values is my reviews, there is a box at the top of each review that contains Wh for different loads.

Calculate the watt-hours at the nominal voltage which is close to the average voltage the battery can provide over its useful capacity. A battery is able to produce more watts when it is fully charged but that max power output potential drops as the battery is discharged.

For both size and weight comparison, a useful graph with a good visual comparison titled; Relative Energy Density of Some Common Secondary Cell Chemistries
can be found near bottom of page https://www.mpoweruk.com/chemistries.htm

HKJ said:

For Alkaline batteries the energy varies significantly with load current.
You best way to get comparable Wh values is my reviews, there is a box at the top of each review that contains Wh for different loads.

Click to expand...

+ 1 - HKJ's reviews are the best resource on the web for this, he has Wh listed at the various loads for all of the batteries he has tested.