On Sun, 19 Nov 2017 01:11:03 +0000, Fredxxx wrote:

snip

It is good that stationary flooded cells gas to some degree when in
the last phase of their charge to prevent electrolyte (and therefore
charge) 'stratification' as the rising bubbles help mix the
electrolyte.

Complex charge regimes usually have an equalisation charge phase where
the intention is to 'overcharge' the battery so it gasses,

As do the most basic transformer based chargers.

hopefully
undoing some of the sulfation

That would be a big *hope* IMHO.

and mixing the electrolyte.

Yes, that is a positive side effect of 'overcharge' gassing.

It's done as a
separate process to absorption and float charging.

Yes, if you break down the phases logically with say a 'Smart' charger
but still happens with a basic charger (to varying degrees, depending
on the terminal battery voltage and the charge / current and voltage
etc), during the end of the absorption phase (the last 10% of the
charge).

snip

Cells do gas not only when charged but when being discharged and that
includes when they are self-discharging. If the OP's battery is only
25% of it's original capacity and whilst it is still functioning, I
wonder if it's self-discharging more than the other batteries he's
comparing it with? shrug

Given the quantities of water the OP says the battery has been
consuming, even a complete self-discharge wouldn't cause 50ml to
disappear from each cell.

I agree. The 8 x Crompton 6V x 200Ah traction monoblocks I was running
in the EV would take that (each) and more if I left the checks for a
bit too long (weeks rather than days) but I'm not sure even they would
lose that (each) when the car was not being used. However, when left
for a couple of years unused, even these large and fairly new
(compared to the OP's battery) batteries lost enough electrolyte to
expose the plates. If I checked them again now, all the cells are
probably bone dry. ;-(

Now, that is either from evaporation or the plastic battery cases
being gas-permeable to some degree (as is much plastic) and it's (the
water) simply leaving as gas (H2O)?

Cheers, T i m