Why can't new and old Yuasa batteries run in series and parallel

New batteries have more chemical reactants, higher terminal voltage and smaller internal resistance, while old batteries have lower terminal voltage and larger internal resistance. Generally, the internal resistance of 12V new batteries is 0.015-0.018 ohms.
Because people are not very familiar with the use of batteries, there will be some errors in the use of yuasa Battery. For example, when new and old batteries are used in series and parallel, it is unknown that this method will shorten the service life of new batteries.
Because the new batteries have more chemical reaction materials, higher terminal voltage, smaller internal resistance, lower terminal voltage of old batteries and larger internal resistance. Generally speaking, the internal resistance of the new 12V battery is 0.015-0.018 ohms, while that of the old battery is very large. If the old and new batteries are used in series, the charging voltage at both ends of the old batteries will be higher than the charging voltage at both ends of the new batteries. The effect is whether the new batteries are full and the old batteries are too high. In the discharge state, because the capacity of the new batteries is larger than that of the old batteries, the effect is the old batteries. Overdischarge, even old batteries are reversed, and the battery expands to form side effects. It will lose the power of new batteries, coupled with unstable voltage inside the appliances, and there is a risk of overusing old batteries.