[branko_d]

> lead-acid's very low risk of fire

Isn't lead-acid prone to releasing hydrogen gas?

When jump-starting a car, it is commonly recommended to connect the ground (black) cable to the chassis, not to the battery's black terminal, to avoid a spark igniting the hydrogen and causing an explosion.

[tempay]

The lead-acid batteries used in data centres are normally "sealed lead-acid batteries" and release significantly less hydrogen.

See: https://en.wikipedia.org/wiki/VRLA_battery

[doggodaddo78]

Wikipedia is wrong. VRLAs aren't SLAs, and vice-versa. Actual SLAs are very, very expensive. All VRLAs can vent, by definition.

VRLAs can overcharge and catch fire just like flooded batteries. They just don't go kaboom as much or spray acid everywhere. When having thousands of batteries in a room, one of them catching fire is inevitable. This is why batteries are in separate fire containment rooms, on nonflammable shelving, in redundant strings, and protected by FM200.

[Nextgrid]

Isn't hydrogen produced only while the battery is charging, or at worst, when discharging? If so, this still makes them much safer as they're otherwise inert while not in operation, compared to lithium-polymer which contains materials flammable at all times.

[rootusrootus]

LiPo and LFP are very different things. LiPo is probably the biggest fire risk battery chemistry in common use today. LFP is pretty safe. LTO even more so.

[Nextgrid]

Yes, I am aware of other "L" batteries that are safer. I was just commenting about how lead-acid is still relatively inert compared to the "fiery" kind of L batteries.