I have a small portable device that is powered by 4 alkaline AA batteries.
After X hours of usage, I see the "low battery" indicator flashing. At that point I assume that all 4 batteries are ~5% full (or something).
What happens if don't have 4 new batteries but only 2? So in the device I end up with:
- 5% full battery
- 5% full battery
- 100% full battery (new)
- 100% full battery (new)
Will the device display the "low battery" indicator after X/2 time of usage? Or is there a possibility that it'll go through the new batteries at a faster rate, thus I should always try to replace all 4 batteries instead of just 2?
Also, will the device at that point think that it's 50% full? Does it work that way?
Best Answer
Alkaline cells have essentially no energy at about 0.8V. This means that 4 cells would be about 6V at full and 3.2V at empty. "Low battery" is usually about 1V or so. This means that the device would be supplied with about 4.1V total. This represents about 35% full.
The next hurdle is that all four cells will keep discharging, and once they hit 0.8V they rapidly crash down to 0V. This means that the supply voltage will suddenly drop to below 3V. There is no guarantee that the device will continue working with such a low voltage, and if it did, there is also no guarantee that the good cells can force enough current through the dead cells to keep the device running.
And now the next bit of bad news. Since current is being forced through now completely dead cells, they can take on a reversed polarity. This can lead to physical damage of the battery, including but not limited to leakage of corrosive material.