I bought a "1 million candlepower" lead acid battery spotlight &
charger some years ago (for 2 GBP), and it's given very good service.
The instructions stated that it could be recharged only 25 times.
The battery has at last given up would not hold a charge.

I opened it up and discovered that the battery had three rubber caps
over the vent holes. I removed these and filled the holes with
distilled water. It seemed to soak up lots of water.
After a charge it's as good as new again.
If you try this, don't try the first charge with the rubber caps on,
as they will pop off and fly around the room!