# Are sealed lead-acid batteries safe to use indoors?

I have a small, 12V sealed lead-acid battery. I know regular lead-acid batteries can be dangerous to use or charge indoors, due to the fumes they release and the potential for acid to leak out or spill. A sealed lead-acid battery wont release fumes or spill though, correct? Does this make it safe to use/charge indoors?

Thank you!

• Gel cells and AGM batteries are relatively safe to use indoors. They cannot spill, and do not give off hydrogen when charged properly. I don't think I would recharge a liquid-electrolyte sealed lead acid battery indoors unless it had dedicated ventilation. (You could put the battery in a box, and vent the box to the outdoors... put the vent high, since hydrogen is lighter than air). If you have a drafty barn or shed or garage, then it is probably fine. Depending on what you are doing, you may want to check what is required to satisfy building codes. – mkeith Jun 16 '15 at 3:41
• Note that depending on their charge state, their temperature of freezing varies. Lead-acid batteries should never freeze, it is very hard on them. – rdtsc Sep 24 '15 at 19:16

Actually SLA batteries have a vent... so the name "sealed" is a bit of a misnomer. VRLA (valve-regulated lead-acid battery) is actually a name for the same tech.

Practically every UPS (uninterruptible power supply) I know of has one [or more] SLA[s] inside, so it's generally safe for indoor use. Here's a snippet from an APC white paper on the issue:

Valve regulated lead acid (VRLA) batteries [...] do not require special battery rooms and are suitable for use in an office environment. Air changes designed for human occupancy normally exceed the requirements for VRLA [...] ventilation. Vented (flooded) batteries, which release hydrogen gas continuously, require a dedicated battery room with ventilation separate from the rest of the building.

And bit later in the paper the difference in gas output is quantified as 60 times less for VRLA:

VRLA batteries are considered to be “sealed” because they normally do not allow for the addition or loss of liquid. A vented battery can give off sixty times more gas than a VRLA battery in normal use.

And the reason for this is that in a "sealed"/VRLA battery:

hydrogen recombines under pressure with oxygen into water inside the battery. Gas can only escape when internal pressure exceeds the rating of the pressure valve.

The fact that they're pressurized explains why in extreme cases of misuse or abuse they end up seriously bulged. The plastic container is actually designed to cope with that scenario.

Also, small SLAs (almost certainly the one you have) use gel as electrolyte suspender so won't spill liquid[s] even if cracked. The larger ones use a glass mat instead (gel is rather expensive).

Yes, sealed-lead batteries are considered safe for indoor use -- they are no different from dry cells or NiCds in that regard, and can be found in emergency lights and other applications where low cost and relatively long livespan in float applications is critical.

With that in mind, it is possible (although unlikely) to encounter leakage if they are left untended for very long periods of time (just like dry cells).

"Safe" is a relative term. I charged a flashlight that contained 2 6v lead acid batteries inside the flashlight ON my laminate kitchen counter. The next day I noticed a pool of liquid below the flashlight. The acid escaped from the batteries and leaked ON the counter. It discolored the laminate to a lighter white color with no way to restore the original color pattern. I now have a $3000 counter replacement ahead of me. Was I safe? Oh yea, definitely safe. No physical harm at all. • Yeah -- I've seen small SLAs in emergency lights leak before (as I alluded to in my answer). Worst that happened was having to clean my hands repeatedly, and a ruined shirt. – ThreePhaseEel Oct 14 '16 at 21:20 • Can you apply dilute sulphuric acid to the rest of the counter to lighten it to the same shade? It will save you about$2995. Although I think that is more for diy.stackexchange.com. – Andrew Morton Oct 14 '16 at 21:26