Yep.
From my experience, if the S/S doesn't work, it means the battery has had it.
No charging of it will help.
The battery needs to be fully charged almost permanently. Leaving it alone won't work, and by the time it's been sitting around and perhaps partly charged, it'll be knackered in maybe three years.
It will still function perfectly as a car battery, and still be absolutely fine at starting even in the coldest conditions, but what it won't do, is perform as a S/S battery.
Dunno why, and I can't find anything written down or find anyone who can test a S/S battery properly.
Only option, is to buy a new S/S battery, or forget the S/S ever working.
Good luck,
Mick.