ORIGINAL: opjose
Over drawn or over charged sealed batteries also tend to "inflate" first.
The gas produce causes the plastic casing to inflate like a puffer fish.
When you see a small amount of this, it's time to replace the battery.
Good advice!
I'm trying to revive some near new SLA's that I recovered from a toasted UPS at work. The batteries appear to have taken a hit during the UPS failure so I'm being very cautious in trying to charge them. If I see the slightest swelling they will immediately go to the recycler. With luck, they may just need a good cycle or two (hoping anyway).