Why the rechargeable 1.5V Li-ion battery is rated with mWh instead of mAh?

XTAR Light

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mWh and mAh are related. The mWh is the result of multiplying mAh by the voltage of the system. You may find the rechargeable 1.5V Li-ion battery is rated with mWh instead of mAh. Because the voltage of this battery remains constant 1.5V until it's almost completely discharged. It means that the energy stored in a rechargeable 1.5V Li-ion battery is proportional to the product of the voltage and the capacity, which is expressed in mWh. As for other types of rechargeable batteries, such as 1.2V NiMH batteries, have a variable voltage during discharge, which makes it more suitable to express their capacity in terms of mAh.

Some people compare the capacity and discharge time of the rechargeable 1.5V Li-ion AA/AAA batteries & 1.2V NiMH AA/AAA batteries. They may think the 1.5V Li-ion batteries are not so preferable to NiMH batteries. But the 1.5V Li-ion batteries keep constant 1.5V output. The discharge voltage of the NiMH batteries continue to drop during usage. So we can't do a simple formula conversion and make comparison. The overall performance is more important.

For devices that require a steady and stable high-voltage output over a long period of time, they are definitely stronger with 1.5V Li-ion batteries. Such as, RC cars, VR controllers, digital cameras, blood pressure meters, some smart household appliance etc. They may consider 1.2V NiMH a low or dead battery, and constantly need to replace new battery. The 1.5V Li-ion batteries can maintain more stable performance.
 

alpg88

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It is a marketing trick, 90%+ of people have no idea what mwh and mah mean, but they do understand a bigger number is better, and mwh always show a larger number than mah.
 

Dave_H

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I believe mWh or Wh is more accurate measure of what's available at the load end, as long as it's reported accurately. What is consistently misleading is USB battery packs which specify the Ah capacity of the cell(s) at the cell voltage; whereas this capacity is not fully available at the output due to up-conversion and loss in the circuit. Assuming 90% efficiency (which may be optimistic), overall only about 2/3 of Ah cell capacity is available at 5v (average cell voltage 3.7v).

Dave
 

alpg88

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I believe it makes no difference as far as accuracy, mwh rating they put on 1.5v cells is the same as if you would calculate it based on li ion cell voltage and capacity. I do realize putting capacity of the li ion cell would be misleading since there is a buck circuit there. but if you convert their mwh to mah based on 1.5v vs 3.7. you would get smaller number. mah allow people compare capacities, since new 1,5v li ion are replacing 1.5 alkaline cells that rates capacity in mah. most people would not catch the difference of mwh and mah, they would believe new cell has more capacity, contrary to what real capacity is.
 

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alpg88

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Oh, there is another aspect, actual true capacity, it depends on fully charged voltage, and cut off voltage, and circuit efficiency. do they terminate charge at 4.2v, 4.0v? do they cut off at 3v, 2.5v?? we do not know for sure. but it can change the number dramatically. that is why i bought 5 different kinds of li ion AA and even D cell, to test them take them apart, measure actual voltage of the li ion cell inside. voltage under load.........ect, it'll probably take few weeks untill i get all the cells, and charger, some cells have a usb port some do not
 
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