if your device is failing, replace all the batteries， Do not mix old and new batteries
December 28, 2020
We’ve all experienced the frustration of our small batteries failing. Whether they’re powering children’s toys, remote controls, smoke detectors, or even salt and pepper grinders, we seem to be replacing the batteries every other week.
Most of these types of devices rely on more than one battery. It’s common to open up the back of the device, remove the batteries and then replace them in a different order. This can give you a bit more time before needing replacements and should cause no harm to the device. You feel quite smug and as though you out-smarted the problem, but it’s short-lived.
It can be tempting to replace one of the old batteries with a new one, leaving the other old ones in place. People do this in an attempt to save money, and while it might appear to work, there can be a cost due to a range of issues:
Let’s assume a device requires two AA batteries. New batteries will power the device for (say) 24 hours. If we assume that the old batteries are 50% drained, replacing just one battery will result in the pair only lasting 12 hours. Then you need to replace the old battery, but which one was it? If you’re unsure, now you’ve wasted half of the new battery as well as the old. Even if you know which was which, you do it again and the same problem arises. Instead of replacing batteries after 24 hours of use, you’re always replacing them after only 12 hours.
Some devices are sensitive to voltage. By combining an old and a new battery, the voltage will be lower and the device will be less effective. A torch might be less bright, or a remote control might need to be pointed at exactly the right angle to work properly.
Older batteries degrade faster than newer ones, so if unused for a period of time they have a higher likelihood of leaking. This, of course, can damage your device.
As batteries discharge, their internal resistance increases. This means that an old battery will have higher internal resistance than the new battery, and will inhibit the passage of current so the performance of the device becomes poor.
In the worst case, when older batteries no longer contribute to the current they begin to consume the current passing through, and this can lead to overheating which could cause a fire.
Replacing the batteries doesn’t have to be as expensive as you think. So in short, if your device is failing, replace all the batteries at once. You’ll get better performance, longer life, and problem-free operation of your device.