Battery conditioner/charger question

[Washburn]

Last month, as it started to get colder, just for the peace of mind, I bought a jump-starter and a Noco Genius 3500 batter charger/maintainer/conditioner whatever that is...
It's hooked up to the battery to help it a bit as I don't drive the car very often...
When I 1st hooked the Noco Genius up, it went from 25 to 50 to 75% within about 25 minutes but then took about 7 hrs to get to 100%...but i guess it does the charging/conditioning slowly on purpose....

Noco recommends keeping it connected with adequate ventilation - (does not overcharge - it's one of those 'smart' conditioners) during cold weather and seldom driving so that it can be on maintenence mode, making te battery is always in top condition...

So....Can I just keep the Noco conditioner/charger connected to the battery while the trunk is closed (the car is inside a garage)
Or should I keep the trunk open while the Noco is connected in maintenance mode? (with garage still closed)
The 1st time I used it, I had the trunk open and the conditioner connected with the garage closed overnight to condition the battery a bit after it charged the battery...no problems, but I disconnected it the next AM. My question is about keeping it connected for long(er) periods on maintenance mode while the car is sitting ...

[LivesNearCostco]

I don't think it matters if the trunk is open or closed, as long as your battery vent tube is properly connected. Charging batteries can generate explosive hydrogen gas, but H2 is light and disperses quickly, so I think it's only dangerous when you're doing a rapid or heavy charge. The vent tube should vent any H2 gas out of the trunk and under trickle charge it should dissipate out of your garage fast enough that your water heater or light switches won't ignite it.

But follow this answer at your own risk! If your garage is sealed up really tight, or you do a heavy charge, or your water heater doesn't have a shielded combustion chamber, it could pose a risk. The other reason they might say use with adequate ventilation is to prevent the charger from overheating.

[ryankokesh]

So the battery vent tube is for h2?


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[LivesNearCostco]

I assumed... maybe it's really for extra sulfuric acid?

If it is for gas, when the battery in the engine compartment, it's usually pretty well ventilated so no vent tube is needed. The trunk is not always well ventilated.

[mjweimer]

You are correct, the vent is designed to vent Hydrogen gas generated during the discharge/charge cycle. If you are unlucky the acid in the battery can be vented but I have only seen this happen after someone grossly overcharged/overheated their battery on an old school high amperage battery charger.

I have successfully left several different cars on a trickle charger and in the garage for months at a time with no ill effects.