SLA battery fail?

[Tiny]

Hey all, on old friend brought over a SLA motorcycle battery that he'd had stored in his shed on a shelf for ~10 years. It was one of the type that is dry, then you add the acid pack & seal it.
He doesn't have the ability to charge it, so brought it to me. Mister fix everything for the neighbours.

Obviously never had acid in it therefore not used before. The seals were fully intact.
I had to remove the metal tape seal, insert the acid pack, then push the final seal plug strip on.
The instructions, said wait 20 minutes before charging @0.1c. 9AH battery = 0.9AH charging rate which I can accommodate.

Never got to charging it.
After doing the acid & seal, I checked it at around 10 mins & it was warm to the touch, hmm exothermic chemical reaction in process.
After 15 mins it was warmer, not what I'd call hot = say 40c, to the touch & swelling at both ends, not the top, bottom or the sides.
Instantly moved it to a safe location. Checked voltage at terminals 11.88v.

It only swelled slightly, then cooled off. Not game to put it on a charger. I think it's not recoverable.

I thought with dry storage, unused, it should be fine, but 10 years is a long time in an LA batteries life.

Other factors include that his storage shed would be subject to below zero temps (-5C) every winter.
I think this was probably the killer.¯\_(ツ)_/¯

What do you think?

[wotnot]

Found this...

[Tiny]

Thanks, I think the critical here was cold temperatures & age, which has caused the negative plates to oxidise. It may actually be salvageable, but the mild swelling is concerning.
Not worth the risk. he's bought a new one pre-activated for $120

Shelf life of a dry charge battery will vary, but may be kept for several years under ideal conditions. Store in a cool dry area. The positive plate has an unlimited shelf life. The negative plate will revert to lead oxide when in the presence of water and oxygen. If this should happen, the battery is not ruined, but activation will take considerably longer.
The electrolyte temperature will rise dramatically during activation. Do not place on charge until the temperature drops below 115° F. Activation may take several days.