Thu. Jun 13th, 2024

Key Takeaways

  • Battery levels are calculated based on voltage output, affecting how charge percentages are estimated.
  • Alkaline and lithium batteries have different voltage discharge curves.
  • Use alkaline batteries in devices designed for them to prevent inaccurate battery level readings.

If you’ve put a lithium AA battery into something like a gaming controller or any device with a battery meter meant for alkaline batteries, you may notice that the batteries seem to go dead suddenly, even if the meter still showing a full battery right up to the end. Why does this happen? The answer is surprisingly simple.

How Battery Levels Are Calculated

As the charge in a battery depletes, the amount of voltage it puts out also declines. If you know how much the voltage will go down from full to empty, then you can peg the battery percentage to the current voltage level.

There are other ways to calculate battery charge, but these are usually reserved for built-in batteries, where the manufacturer knows exactly what type of battery is inside the device, and can then estimate its level based on a record of how much energy went into and out of it, or by using algorithms that observe how the battery behaves. These sorts of battery level management methods require complicated battery management software and hardware that obviously won’t be found inside an AA battery, so for most gadgets that take AA batteries it’s going to be a question of current voltage equaling a certain battery percentage estimate.

Alkaline and Lithium Batteries Have Different Voltage Discharge Curves

This is where the major clue lies in how lithium AA batteries behave in devices that were designed with alkaline batteries in mind. Both types of battery will provide the correct voltage range for those devices. AA batteries are usually in the 1.2V to 1.5V range, depending on the exact battery chemistry. For example, Nickel-Cadmium (NiCd) batteries have a nominal voltage of 1.2V and alkaline batteries have 1.5V. Lithium AA batteries also have a nominal voltage of 1.5V, so from the device’s perspective, it’s all good, with the right level of power delivered.

However, there’s a big difference in how the voltage output of an alkaline battery drops compared to a lithium battery. An alkaline battery has a gradual and predictable drop as it discharges. A lithium battery, on the other hand, will provide its nominal voltage right up to just before the battery is depleted, after which the voltage drops suddenly.

That’s why your lithium AA batteries seem to report a full or nearly full battery right up to the second they die. It’s quite annoying while playing a video game, but for some devices, this can be a more serious or inconvenient issue.

Avoid Lithium Batteries for These Devices

While it’s fine to use lithium AA batteries in any device designed for AA batteries, this battery level issue can be quite a pain in some cases. For example, imagine you’re checking the battery level on a walkie-talkie or a digital camera before you leave the house, and it seems full, only to be left in the lurch a few minutes after using it. Likewise, if you have a smoke alarm that was designed for use with alkaline batteries, it may not give you the low battery warning early enough. If you want the benefits of lithium battery technology in a device like a smoke detector, it’s best to buy a smoke detector designed for it. For example, a 10-year sealed battery smoke detector knows exactly when its battery is about to die.

The most important thing to know is that a lithium battery used in a device designed for alkaline batteries may result in inaccurate battery level information. If you use them on a device with no battery meter, it’s no big deal. However, if an accurate battery level is important, then it’s best to stick with exactly the type of battery the manufacturer intended.

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By John P.

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