Or maybe better said, a question about a small battery.

Not for a Vanagon, but I hope to garner some list wisdom and maybe help
someone else with the knowledge in the future.

I have an ATV/motorsport battery (9BS) that is acting strange.

It shows 12.6V at rest, but drops to about 0.13V when any load is applied,
even a 12V lightbulb.

I popped the caps and the electrolyte was very low in all the cells.  The
plates looked pretty clean so I bought some battery acid and filled it up.

Gave it a 2amp charge until indicated fully charged, about 4-5 hours later.
Now my test light burns bright- promising.

However, when installed in my motorcycle, it cranks half a turn and dies.

So, the battery is probably damaged even though the inside looks pretty
good, from what I can see.

Just thought maybe someone here has some experience with bringing batteries
like this back to life.

Any help or advice before I buy a new battery is appreciated.