When a battery wears, it tends to get a drop on voltage and an internal resistance that increases. The net effect is that the old battery's output isn't quite up to the mark, and it may have many bad effects, including wearing out the new battery, leakage or worse situation.
As most devices require batteries in series. If you insert one old battery (50%) with one new battery into the device, assuming the current drain remains the same, the old battery will run out after half the usual time. Unless you marked them or can measure them afterwards, you will have to throw out both batteries. Which means you have wasted half a perfectly good battery.
If the device is sensitive to voltage, such as in a flashlight, the combination of new & old batteries will start at 2.85V (e.g.1.5V+1.35V) instead of 3V. The light may be less bright even at the beginning. So the performance is not good. Besides, old batteries tend to degrade chemically faster than new batteries. If you keep them in the device unused for a long time, you may find that the old battery may leak after a few months, ruining your device, which is also dangerous.
It's suggested to replace your batteries as a set, to recharge them all on the same cycle. Some users put a bit of coloured enamel paint on their rechargeable batteries, blue, yellow, green, red etc, so you will know which sets are which and charge them together. And it's also better to prepare a set of new batteries than mix old and new.
As most devices require batteries in series. If you insert one old battery (50%) with one new battery into the device, assuming the current drain remains the same, the old battery will run out after half the usual time. Unless you marked them or can measure them afterwards, you will have to throw out both batteries. Which means you have wasted half a perfectly good battery.
If the device is sensitive to voltage, such as in a flashlight, the combination of new & old batteries will start at 2.85V (e.g.1.5V+1.35V) instead of 3V. The light may be less bright even at the beginning. So the performance is not good. Besides, old batteries tend to degrade chemically faster than new batteries. If you keep them in the device unused for a long time, you may find that the old battery may leak after a few months, ruining your device, which is also dangerous.
It's suggested to replace your batteries as a set, to recharge them all on the same cycle. Some users put a bit of coloured enamel paint on their rechargeable batteries, blue, yellow, green, red etc, so you will know which sets are which and charge them together. And it's also better to prepare a set of new batteries than mix old and new.
