Why were they dry to beging with?
Well fast charging gasses them What is fast?
A pair of GC-2 are 220 amp horus give or take, anyting over 66 amps is FAST charging, even less may be (When I had a pair of GC-2 and an 80 amp converter I had to water 'em every spring.. I still have the inverter, still have a pair of 230 amp hour GC-2. plus some additional capaity, now water 'em every few years (2 months shy of 4)
also equalization charge will gas 'em a bit.
You might limit your charge current to 20% C/20 capacity
This will REDUCE gassing (boiling off of water)
Now, next, the fan
Thermostat controlled may run even when converter/charger or Inverter OFF.
I've had the SUN fire up the fan on my converter many times.