A single cell battery is composed of electrodes and electrolytes, which form the basic unit of the battery pack and is called a single cell battery. How to measure the voltage of a single battery? We usually use mechanical relay method for isolation detection, differential amplifier method for isolation detection, voltage divider method for isolation detection, photoelectric relay method, and other methods for measuring the voltage of a single battery. The mechanical relay method can directly measure the voltage of each individual battery, but the mechanical relay has limited service life and slow action speed, and is not suitable for use in long-term rapid inspection processes. The measurement error of the differential amplifier isolation method is basically determined by the error of the isolation amplifier, but due to the high measurement cost of each circuit, it is slightly insufficient in terms of economy. The voltage divider method has fast response speed and low measurement cost, but its disadvantages are that it cannot adjust the divider ratio well and the measurement accuracy is not satisfactory. The photoelectric relay method has fast response speed, long working life, relatively low measurement cost, no switch contacts, and can play a role in voltage isolation. If the selected photoelectric relay adopts PhotoMOS technology, it can achieve high measurement accuracy. Therefore, the photoelectric relay isolation method is an ideal method for measuring the voltage of individual batteries. The voltage measurement method for single cell batteries in this article is based on the isolation method of photoelectric relays. The on-off control strategy of photoelectric relays is an important issue to be solved by the isolation method of photoelectric relays. The commonly used on-off control methods for photoelectric relays include: I/O direct control, decoder control, analog switch control, etc. The direct control method for I/O is simple and easy to implement, but it requires a large amount of I/O resources. The idea of decoder control and analog switch control is similar, that is, using a small number of I/O to control a large number of photoelectric relays, these two methods reduce the occupation of I/O ports. The use of I/O direct control, decoder control, and analog switch control requires the design of the on/off control circuit, A/D conversion circuit, and processor on the same module, namely the sampling module. In this way, the two electrodes of a single battery need to be led to the sampling module, and the entire battery pack will have a large number of wires connected to the sampling module, resulting in cumbersome installation and complex electrical wiring. The measurement of individual battery voltage should focus on solving three problems: using electrical isolation between on-site and measurement systems, reducing costs and simplifying design solutions, and improving system accuracy. The on/off control methods of I/O direct control, decoder control, and analog switch control for optoelectronic relays lack simplicity in design