When you connect two in parallel, the higher one will try to charge the lower one. It's going to depend on the voltage of the lowest battery as well as the relative voltage difference. As a battery gets closer to full charge, it will want less current, and the current it wants will depend on how many cells in parallel.
I've got 36V 10S-2P batteries that I often connect in parallel. I used to make sure my voltages were exact when connecting in parallel, but after measuring the currents, I believe a 0.3V difference was negligible when both are near full charge. I just re-took these measurements, using my y-connector and a Tenergy wattmeter on the higher battery.
-Two 10S-2P batteries at 42.0V and 41.7V, a .30v delta. Connected in parallel, I'm seeing .25 amps flow into the lower one.
-Two batteries at 41.9V and 40.8V, a 1.1V delta. In parallel, I am seeing 1.0 amps flow into the lower battery.
If the lower battery had been a 10S-20P, it would draw 10X the current of a 10S-2P. Hence 20A at a 1 volt differential. Not good at all.
You'll have to consider carefully what you do. I always check voltages before I do this. You never know what you might have on a battery.