Usually they are OK upright or on their side, but not upside down, as there is a small risk that the over-pressure vent may not work properly if they are mounted this way.
Can a UPS battery be used upside down?
Safety considerations depend on the battery manufacturer's recommendation. Theoretically, they should work in any orientation. But only the manufacturers know how they have constructed the battery and whether they can be used upside down. OR Novel Idea - just lay the UPS on its side. I found this
If no sign, it'll be fine. The major fear of putting a lead-acid battery on its side is it spilling sulfuric acid onto wherever it might end up. It won't hurt the battery itself, other than if it loses acid. If you are sure no acid has leaked, then it's probably a case of "no harm; no foul" and you got lucky.
Can acid escape from a battery vent?
Acid can still escape from the vent if the battery is put into a position where the acid can escape through the vent. Depends on the battery type what bad can happen, but generally that doesn't include harm to the battery -- it includes danger of acid leaks. Sealed, maintenance-free doesn't mean anything.
Can you put a battery on a side?
So it's usually a choice between liquid acid and AGM. If your battery is liquid acid type, even if sealed and maintenance-free, keep it upright all of the time. Don't put it on its side or you may get leaked acid. AGM, you can perfectly well put these on the side. Usually charging when completely inverted though isn't permitted.
Is a sulphuric acid battery a leak?
Sulphuric acid is pretty strong acid so you should still treat a potential leak as a leak. As mentioned, agm batteries like Optima and a few other less well known are popular for off road where the battery can be mounted upside down or sideways. Completely sealed.
What happens if you invert a battery?
In permanently sealed liquid acid batteries, the acid is liquid. It will flow out when inverted. In gel batteries, the acid is gel. It won't flow at all. You can invert the battery and it stays as gel. But charging when inverted, it's possible some of that gel is pushed out if hydrogen gas is created and builds up pressure.