VSR switching repeatedly, does it damage battery

Hi,

my solar panel and alternator both feed into a starter battery. Which is connected to a leisure battery through a VSR (Voltage Sensitive Relay).

In the morning the voltage in the solar panel goes up, and when the starter battery reaches 12.9V, then the VSR connects the two batteries. At that moment, the starter battery being quite full and the leisure quite empty, a high current goes to the leisure battery, and both batteries voltage comes down to about 12.6V or 12.8V. Which stops the VSR, so the batteries get disconnected again. And the same cycle starts again every few seconds.

This has probably been going on for months without noticing, and now my question is: is this one of the reasons why my leisure battery is loved? (probably sulfated, and quite possibly also stratified)
Also, how do you call these cycles? "VSR cycles"? I couldn't find anything about it online.

I know that the battery has been both overcharged and undercharged in the past, so I know that this VSR problem has not caused the whole decay.

And I also know how to make things better: by wiring both the solar panels and VSR sensor to the leisure battery instead of the starter battery; because the starter battery's voltage is almost never low, so I won't get this large drop when it gets connected.

My goal here is to learn about battery decay and care.