The 9V battery in the multimeter has a measured voltage of 9.3V, but it doesn't work anymore
This needs to be elaborated on in two aspects. Because 9V stacked batteries are divided into carbon based batteries and alkaline batteries!
1. Carbon batteries have a high instantaneous current, but not for a long time! The key is cheap! If you don't use it and leave it for one or two months, it will basically consume a lot of electricity. When you run out of battery and the battery is low, replace it with a backup battery and find that it hasn't been used for long and then runs out of battery. The specific manifestation is that when the multimeter displays, there are no words left. It can be displayed again when turned off and then on. Remove the measured voltage, there is an 8V voltage.
2. Alkaline batteries have stable output and long lifespan, making them very suitable for multimeter use. I used to use carbon batteries, which cost several yuan a year. Since replacing the alkaline battery with a well-known domestic brand, there has been no such malfunction as yours. Think about it, the voltage resistance is being detected, and the multimeter is running low, resulting in a significant error. How deceitful is it? The low discharge characteristic of alkaline batteries enables their long-term storage. Shelf life of 10 years, store with confidence.
Check if a battery is charged, not by voltage, but by current. As long as the battery can draw a certain amount of current, it can still be used, regardless of the voltage.
Voltage is just a potential difference, it only indicates that there is a potential difference between these two places, and having a potential difference does not necessarily mean that there will be a current. For example, when a battery is empty, there will be a potential difference between the two electrodes, but there is no current because there is no conductor to form a circuit.
What if there is a circuit? The most extreme scenario is to directly connect the two ends of the electrode with a wire (such as copper wire), and at this point, there should be a large amount of current. After all, the resistance of the conductor (copper wire) is very small, according to Ohm's law, the current is definitely not small, but the actual situation is not that. This is because the battery, as a power source, also has a resistance, which is relatively large (relative to the wire), The current that the battery can provide is also constrained by this resistance.
When the battery is used or discharged for a period of time, the internal resistance inside the battery will increase, and the final result is that there is not much current to be pulled out. Although voltage can still be measured when unloaded, when you connect the load to pull out the current, the voltage will quickly drop due to internal resistance, ultimately causing the battery to be unable to supply power normally.
In order to solve this problem, some people used to inject salt water into the battery to reduce internal resistance and restore the battery's power supply capacity within a certain period of time. However, when the medicine or electrode reaction inside the battery is depleted, injecting anything into the battery is useless.
If your 9V battery runs fast, it is recommended to use a rechargeable battery, that is, a regular battery, or the freshest battery. All batteries have a factory date, but some people may use old batteries or even used batteries to be repackaged, so the location of the battery purchase is also important.
