The charger wasn't telling me the battery was dead.

For fifteen years, I treated that refusal like a verdict. Low number. No charge. Replace the battery.

What I eventually learned was that many automatic chargers stop before they ever determine whether a low-voltage battery is still recoverable. They see a number below their cutoff and refuse to begin.

That does not mean every old battery can be saved. It means the charger's refusal is not the same thing as proof that the battery is finished.

The missing step was learning how to tell the difference — and how to put a controlled charge back into the ones that still had life left.