they still vent i believe

Thanks for the reply. I'm hoping I can get more details to assess the risk. It is a small Japanese sealed car battery on a low-voltage UPS that trickle charges a couple amps or so and the room is a normal office space that is not at all air-tight where a door is usually open. The battery would be fully charged most of the time unless there has been a power failure.

Hi, all lead acid batterys will vent hydrogen when charging, however the low trickle rate of this type of setup means the rate of venting is low enough that normal to low room air movement is sufficient to keep the level low.

A UPS application takes this into account, but there would be an assumption that the room had some air movement, ie not tight as a drum.

Cyril

Thanks. That's exactly what I wanted to know. It is a draughty old house so I don't think accumulation would be an issue, but I just wanted to make sure.