It is now fully understood what are the consequences of gassing. Excessive gassing would be vented out resulting in a permanent loss of water which makes the battery less efficient (electrolyte chemistry being out of the optimum balance). The gasses retained within the battery air space would recombine into water and return to the electrolyte. Since electricity caused the water to go gaseous, it would be logical to deduce that the gasses recombined back into water would produce electricity. The rate of recombining would be slow, and the electricity produced would not have much capacity. The mythical "surface charge" is basically the electricity produced by the gases returning to the electrolyte. The "surface" referred to is in fact the electrolyte surface in contact with the air space. The surface charge produces a higher voltage reading for the battery that would dissipate over time. Any process that depends on the voltage reading would be thrown off track.
A phenomenon observed earlier in the thread, where the battery continued to be charged even when no charger is connected, is in fact the surface charge charging the battery.
Back to the battery: even at minimal charge current, there remain a tiny bit of gassing. This will dissipate eventually, the dropping voltage over the past few readings suggests the surface charge is being depleted. The surface charge acts as a second charger. In effect, the battery is getting more current than what is available at the moment from the physical charger.
Battery state
13.42v stand alone
13.53v connected to charger
Tiny bit of gassing while connected to charger
6.96 m-Ohm internal resistance
62% wear life (based on 435EN 475CCA)
373 CCA
Spec: Powerline 075 435EN 45Ah(C20), very old
Charger state (halved current from previous to reduce gassing)
25mA effective charge current
0.34w max effective charge power
1.5w mains draw
32.45v open circuit
33mA open circuit