A pair of t-105s is 232 AH capacity. Trojan recommends a 10 to 13% charge rate when using a plug in charger.
This would be 23.2 to 30.16 amps. Ideally the charger would max out at 14.8v at 77F as Trojan recommends too.
If one has limited time to recharge, via grid power, or via a generator, then much higher amp charging sources can be used. A 50% depleted pair of t-105s will easily accept 80 amps, and yes they will offgass more when being charged at this high rate as absoprption voltage will be attained much quicker. Yes higher rates are more abusive to a battery, but it is less abusive than starting the next discharge cycle at a lower state of charge, and possibly drawing them even lower the next discharge cycle.
A flooded battery has to offgass to some degree to reach full charge. This " a properly charged flooded battery will not offgass" is utter BS. It will offgass less if charged at a slower rate, but it still has to offgass in the constant voltage/absorption stage. Once it starts offgassing, lowering voltage slightly will lessen the offgassing, but will also increase time required to reach full charge by some unknown degree that is not applicable across all flooded batteries.
. The limit of significant gassing will be different for each battery, different in every temperature and also change as the battery ages. There are no absolutes applicable across all systems in this regard. Personal reports to be valid to another user, need to have some of the variables listed such as battery temperature, initial charge rate and depth of discharge, as well as battery age/ suspected health, at what point bubbling starts, and at what point bubbling becomes more rapid with more larger bubbles. Don't forget eye protection if looking into cells please.
I have a semantics issue with the term bubbling/ boiling in regards to battery charging, but that is a personal issue, as long as people do not believe their battery is getting to 220F and boiling like a pot on a stove.
The charge rate at which the battery attains absorption voltage will have a LOT to due with how much a battery offgasses. Getting upto 14.8 slowly via solar will have the battery offgassing much less than say using a 35 amp charger that will get the battery upto absorption voltage faster and at a lower state of charge.
There are Huge variables to which one cannot apply absolutes. Batteries have a personality, and it changes as they age, and changes with their average depth of discharge, as well as with initial charging amps, and maximum voltage allowed, and temperature, and battery health, and the possible proximity of the nearest locust.
If one were to observe a battery and record all the permutations as to at what time bubbles started to form in the recharge, and at what point it started gassing a lot, while taking specific gravity readings as well as amperage and voltage, then and only then, can one say at which point the battery offgassing will or will not be excessive and possibly an issue, and only in that particular system with those particular batteries in that particular temperature, at that specific depth of discharge with the same charge rate.
Who the F is going to go this far?
And yes, one does not absolutely need to achieve 100% each and every charge, but the battery will last longer the more often it is returned to a true 100% each time it is charged, and for this ideal, offgassing must occur, to some degree.
I do not think I'd bother with a computer fan to exhaust battery gasses with an unrestricted passive vent on top and bottom. With the heating of a charging battery, convection currents will assist gas removal. Battery should not be allowed to ever exceed 120F though, and higher charging rates will cause battery heating, so ventilation to prevent thermal runaway is a good idea if one is able to apply a 25% charge rate or higher AND ambient temperatures are north of 75F
Honestly the bulk of the offgassing is least likely to occur when one is in doors closed, minimal ventilation mode, in most dweller's scenarios.
I personally dislike the smell of a charging battery, and will not have a flooded battery unenclosed and unvented while in the 85%+ charged range and still charging, in the same space in which I inhabit at the time.
Others have no issues with it, and no concerns.
Offgassing has to happen to some degree for a flooded battery to reach full charge. The degree to which offgassing occurs is dependent on the battery, and the charging currents applied/allowed in a specific usage. Blanket statements by those not actively observing their cells during charging, are not applicable to someone else with different batteries at a different level of discharge and a different recharging rate.
Saying for example, my Trojan t-105s start gassing with one small bubble per second 30 minutes after reaching 14.8v at 11.2 amps via 250 watts of solar on june 21 with a morning voltage of 12.2v and a 62 degreef reading is really only applicable/comparable to another person with the same batteries, same level of discharge, same solar wattage and controller setpoints and temperature, and same level of battery health. The guy with half that wattage available, half the battery capacity and a 12v marine battery at that and half the AH consumed overnight, has little in common with the previous system.
As batteries age they will start offgassing earlier in the recharge cycle and be required to be held at absorption voltage for longer to reach full charge. So they use more water, and are more likely to be smelled and irritate the sensitive human.
HUge variables exist as to how much offgassing occurs and when, and it is ever changing throughout the lifespan of the battery.
Scientific types with interest and measurement tools can narrow down how much and when offgassing occurs, and can try to limit the amount to no more than needed, but Average joe or Jane really can't and is at the mercy of their charger/controller settings, which are hopefully adjustable and not a 'one size fits all' algorithm.
The goal for good battery longevity should be attaining as close as possible to 100% state of charge in the time allotted every recharge cycle, and this goal is often opposite of achieving minimal offgassing.
If one is interested in minimizing offgassing, then one needs to not only have adjustable charging sources, but also the will to observe their cells, and measure the currents at which bubbling begins, then be able to control the voltage, and hope that the time/sunlight/ is still available to reach 100% before the next discharge cycle begins.
Or one can just not worry at all about it and replace the batteries whenever they no longer have enough capacity to meet one's overnight needs. The person who only attains absorption voltage late in the day, for an hour is unlikely to ever smell their batteries, but they will be offgassing somewhat, and the controller might even think they are full and flash that soothing green light, But green lights are liars. Confirm SOC with a Hydrometer when the controller drops to float. Most of the time one will observe specific gravity to be well under 1.275, and the deeper the depth of discharge the more likely the SG is going to be lower when that green light comes on to soothe the human waiting for it.
As long is one is not surprised on the day when the capacity has declined to unacceptable limits, and one gets an acceptable, to them, amount of deep cycles from them before failure, then everything is just fine.
There are more important things than maximizing battery longevity afterall.
Or is there?
