Battery life in hours is the capacity in mAh divided by the device’s draw in mA. Each battery’s mAh in the calculator comes from a named maker’s sheet, with the drain it was rated at.
Battery
Use the current the device’s maker gives, in mA. For microamps, type uA after the number.
Battery life
2,500 mAh ÷ 100 mA = 25 hours. That’s Energizer’s 2,500 mAh for the AA alkaline, at 100 mA to 0.8 V.
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A battery’s mAh depends on the drain
Energizer defines capacity as how long a battery gives service at a specific drain rate down to a specific cutoff voltage. Its handbook drains an alkaline AA at 100 mA. The battery reaches 0.8 V after 25 hours, so it held 2,500 mAh, but a device that stops working at 1.2 V got only 1,500 mAh from it.
Energizer says alkaline batteries are in general more efficient at lower drain rates, and its chart shows an AA giving far more at 25 mA than at 500 mA. Its lithium AA is much less sensitive to the drain rate and the cutoff.
| Battery | Capacity | Rated | Sheet |
|---|---|---|---|
| AA alkaline | 2,500 mAh | At 100 mA to 0.8 V | Energizer |
| AA alkaline | 1,500 mAh | At 100 mA to 1.2 V, for a device that stops at 1.2 V | Energizer |
| AA lithium | 3,600 mAh | At 100 mA to 0.9 V | Energizer |
| AA rechargeable (NiMH) | 2,300 mAh | Rated at 460 mA | Energizer NH15-2300 |
| AAA alkaline | No single figure | Charts by load only | Duracell MN2400 |
| CR2032 | 225 mAh | At 0.2 mA | Panasonic |
| CR2032 | 235 mAh | On a 15,000 ohm load, about 0.2 mA at 3 V, to 2.0 V | Energizer |
| CR2032 | 265 mAh | On a 15,000 ohm load to 2.0 V | Duracell DL/CR2032 |
| CR123A | 1,550 mAh | On a 100 ohm load, about 30 mA at 3 V, to 2 V | Duracell |
| CR2 | 920 mAh | On a 100 ohm load, about 30 mA at 3 V, to 2 V | Duracell DLCR2 |
| 9V alkaline | No single figure | Charts by load only | Energizer 522, Duracell MN1604 |
| 9V rechargeable (NiMH) | 175 mAh | At 35 mA to 1.0 V | Energizer NH22-175 |
A load in ohms is turned into mA at the battery’s 3 V: 15,000 ohms is about 0.2 mA, 100 ohms about 30 mA.
Devices that draw in bursts
A remote or a sensor draws current in short bursts with rests between them. Energizer says a very light duty cycle lets an alkaline battery recover and lasts longer than a steady drain of the same current, but there is no simple equation for how much: only testing shows it.
For a coin cell, Duracell’s DL/CR2032 sheet gives a standard continuous current of 0.3 mA, a maximum of 3 mA, and pulses of up to 50 mA for 1 second.
If a battery is swallowed
If anyone may have swallowed a coin or button battery, don’t delay: call the 24-hour National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222. Keep spare and used coin cells where children can’t reach them.