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While checking the specification of rechargable AAA Ni-MH cells, the specification shows 2 parameters Voltage say 1.2v and Current Capacity say 630 mAh.

However the current capacity is preceded by 'min' For example 1.2v Min 630mAh.

What is the meaning of 'min' here? If I understand the basic Ohms law the load shall only draw the current it needs at a specified voltage. So ideally if I use 630mAh cell or 830mAh cell at 1.2 volts the load shall only draw same amount of current. I hope I am correct.

So indeed what does 'min' specify in such a specification.

Below picture courtesy of Amazon Website.

enter image description here

Thanks.

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It means that the minimum capacity is 630 mAh.

This in turn, for an ideal battery, means that it will supply 630 mA for 1 h, 63 mA for 10 h, 6.3 mA for 100 h, etc.

Real batteries don't perform perfectly. The mAh capacity will depend on the discharge rate and will decrease with increasing current. You may find that the 630 mAh is for the 10 h discharge rate and that at 630 mA the discharge time is < 50 minutes. You will also find that output voltage will drop at higher discharge rates due to internal resistance of the cell.

The test conditions that yielded the 630 mAh capacity should be given on the battery datasheet (which Amazon probably won't supply) along with internal resistance.

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  • \$\begingroup\$ Thank you for the answer. Though I understand that Min stands for Minimum, I am having a tough time interpreting Minimum 630mAh. How does it relate to mAh capacity? Min 2 days would mean it cannot be less than 2 days but in terms of battery capacity it really depends on Load, how much it can draw. From a 630mAh cell load can draw 6.3 mA for 100h or even 1260mAh for just 30 minutes. So how can it be Min 630? That’s my confusion. \$\endgroup\$ – user158365 Jul 29 '17 at 12:54
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    \$\begingroup\$ They're saying that it could be more than 630 mAh but that at a minimum you'll get 630 mAh out of it. Again, buy stuff with published datasheets so that you understand what you're getting and have some guarantees from the manufacturer. \$\endgroup\$ – Transistor Jul 29 '17 at 12:57
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schematic

simulate this circuit – Schematic created using CircuitLab

Let's assume the battery will stay constant 1.2V when there's energy inside. When you connect to a load and draw a constant current of 126mA, current will flow thru R1 for at least 5 hours. That's where you get 126 mA X 5h = 630mAh min.

630mAh min is guarantee by the battery manufacturer, some batteries in actual fact will have 640mAh or even 650mAh. However the manufacturer will claim it at least can output 630mAh.

Once the energy in the battery is depleted, the voltage will fall. In real world applications, do not let rechargeable discharge too much.

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