Removal of Leisure Battery under drivers seat

Hi,
sorry was a new Member earlier this year, but posted nothing.
Had problems getting back onto the Forum, I'm rubbish with passwords!

Getting on well with my 'symphony'.
But maybe a problem with my leisure battery?
4 hours drive back from Devon and 200 miles.
Found Battery not fully charged, had been connected to mains all the time when on site.

Charging it with mains on & van battery charger. Should the charger making a humming noise?
But set off Carbon Monoxide Alarm? Why, I think Hydrogen produced during charging? Seen a comment online. Do i have a fire risk?

Finding access to battery under my drivers seat is almost impossible, and how to remove? Do i have to remove the seat?

Battery is now part charged but cant get it fully charged, as setting off alarm, battery warms up?

DIY or Garage?

Advice please.
Min from LFE

Access to the battery indeed requires removing the drivers seat.
There are four sunken headed allen screws which need removing........you have to slide the seat back and forward and swivel to locate each one.

Do NOT try and lift the seat by yourself....get assistance (experience and very bad back).

Van charger shouldn't particularly make any noise......mine doesn't.
If the battery is not charging when the engine is running, then maybe a fuse has blown.

If the C02 alarm is sounding, it sure sounds like the battery is over gassing.

PB

Doesn't the battery have a vent tube going down through the floor to outside the van?  If not it probably should have. If it's gassing under charge then I'd stop charging it! Particularly if as you say the battery is getting unduly warm, there is an explosion risk. Hydrogen gas is highly combustible in any case so not a great idea to let the van fill with it.