Shame you do not have a clamp on DC ammeter.
I bet if you drained the battery to 50%, set your PM-55 to 13.6v and hooked it up, 55 amps would taper to the 27 range in under 5 minutes, and present no issue to your battery.
Now if you had it set at 14.7v, well perhaps then it might exceed the recombinant abilities and vent.
I've done a lot of observing amperage plugging in my meanwell set to different voltages. i only have 40 amps to work with but anything under 14 volts will have 40 amps begine tapering pretty quickly, and my battery has ~ half the resistance rating of yours, but mine is no longer new and I did not perform these tests on it when new as I did not have the meanwell then.
It really is wonderful to see how much amps flow at different voltages applied. You have the tool to do this, you just require an easier means to see the amps flowing at different voltages.