i did some data logging with the volt pro charger & a standard charger to compare…
results in graph form below!

Each of these tests were performed with a pair of 'permobil' branded VRLA GEL batteries wired in series to 24v
the batteries were discharged for approx 3-5 hours at a rate of ~9 amps before each charge cycle

click to expand each section

what i do not know, is if the charger uses some kinda algorithm to vary each charging cycle.. i.e. only 'equalizing' every few charge cycles, or if its triggered by some 'test' that it preforms on the battery during the charge cycle.. even when running the compatibility mode, one of my test cycles made the batteries pretty warm to the touch (but not HOT)… HOWEVER looking back at the data, nothing was out of spec for 'safe charging practices' during that cycle!

to be safe, i'd avoid leaving the Volt Pro charger connected to a chair for more than 12 hours in the compatibility mode

BTW the 'MK GEL compatibility' mode still charges at 10 amps

regardless of the charger used, i've noticed that the pemobil branded VRLA GEL batteries sometimes will randomly become resistant to float mode charging, and just get warm, and never complete the cycle overnight!
(this happens even without starting the cycle at a low state of charge)
this has happened with my volt pro charger (in mode 1 and mode 3) also with my victron charger, and the gray upright permobil 8 amp charger
in case you're wondering, i did balance both batteries before starting all of this testing

VRLA GEL batteries have slightly different properties and charging needs over traditional Pb batteries
and MUST remain sealed to prevent 'new oxygen' from entering the cells!

regardless of everything - most will agree that 15v or above per battery is TOO HIGH for a daily charging cycle!

if yer bored.. here's the official 'owners manuals'

VoltProChargerManual

Permobil VRLA GEL Battery 'manual'

Permobil Battery MSDS

VoltPro system FAQ Sheet

VoltPro charger "switch settings"