The mixing of old and new batteries is a problem that requires special attention, mainly because their performance parameters may be significantly different, including electromotive force, internal resistance, capacity, etc. The following is a detailed answer to the question of mixing old and new batteries:
1.*EMF Difference**: The EMF of a new battery is usually higher than that of an old battery. If they are used in series, the terminal voltage of the new battery will be higher than that of the old battery, causing the old battery to be overcharged and the new battery to be undercharged. Conversely, when used in parallel, the old battery has a lower electromotive force, which may cause the new battery to over-discharge.
2.*Internal Resistance Difference**: New batteries usually have less internal resistance, while older batteries have greater internal resistance. When the old and new batteries are used together, the battery with large internal resistance may become a bottleneck during charging and discharging, affecting the effect of the entire battery pack.
3.*Capacity Difference**: The capacity of the new battery is usually greater than that of the old battery. If the old and new batteries are used together, during the discharge process, the new battery may be over-discharged due to its large capacity, while the old battery may not be fully discharged due to its small capacity.
4.*Safety Issues**: Old batteries may have safety issues such as leakage and heat generation due to deterioration in performance, and if mixed with new batteries, it may affect the safety of the entire battery pack.
To sum up, there is a big difference in the performance of the old and new batteries, and it is not recommended to mix them. Especially in application scenarios that require high stability and safety, such as new energy vehicles, uninterruptible power supplies (UPS), etc., this principle should be strictly observed. If you must use batteries in different states, it is recommended to consult a professional or operate in strict accordance with the product instructions to ensure the stability and safety of the system.