How much is the voltage of the PLC battery to be replaced with a new one?

Lithium battery for PLC storage, the battery should be replaced when the voltage is lower than 3V.
When the PLC user program is to remain in the RAM, the battery is used. The battery is usually a 3V or 3.6V non-rechargeable lithium battery. The battery life is usually about five years. When the battery is used for a long time, the voltage will be Falling, when it falls below enough to guarantee data in RAM, the program in RAM is lost. If the user does not have a backup program, it will be quite troublesome.
The general PLC has a battery voltage detection circuit inside. When the voltage drops to a certain level, the PLC will alarm and remind the battery to be replaced. The PLC’s instruction manual provides a way to replace the battery. Generally speaking, after the PLC is powered off, because the RAM power supply terminal of the PLC is connected with a charging capacitor, even if the battery is removed, the charging power on the capacitor is sufficient for the data in the RAM to remain for a period of time, so if the battery is removed in a short time (usually 5 minutes) Then replace the new battery, the data will not be lost.
However, the environment in which the user actually uses the PLC is different, for example, the capacity of the capacitor is reduced, and the RAM power supply circuit has
Dust, sludge, etc. form a discharge circuit, which will speed up the discharge speed of the capacitor after the PLC is powered off, thus making the time difficult to grasp. If you replace the battery while charging, you can keep the program safe. Because the power will always
There is a voltage applied to the power supply pin of the RAM chip. Of course, you should also be careful when changing, pay attention to the polarity of the battery and avoid short circuit.
It is best to power on the PLC for 15 minutes (charge the internal capacitor), power off, change the new battery within 5 minutes, and then power on it.