Hi Mick and you are probably right but if you have a large solar panel, say 50w or higher, you might be able to recover the battery.

I use an 80w panel connected directly to the battery. Thats no regulator.

I then leave it "OUTSIDE" for a couple of days to allow the solar panel to "COOK" the battery.

By COOKING or boiling the battery, you can, many occasions, bring a wet cell battery back from the edge.

Note though, you are not likely to get the battery anywhere near it's original capacity.

So consider whether it is worth the trouble to try to recover the battery or just let it fade away peacefully.

Folks PLEASE NOTE, the above can ONLY BE DONE WITH OPEN WET CELL BATTERIES.