CGB looks bad

While the Battery Tender charger was working, I found the CGB CB12170 sealed lead acid battery from the CAO to be not in good health. My DMM showed 8.37 volts coming out of the 17 Ah small battery.

When I connected the BT smart charger, the LED changed to orange. That meant there was a problem...

To verify the charger was OK, I plugged 4-stage charge into my marine gel-tech "B" battery. Got a red light. Yes. Charging. As per normal.

Meanwhile, I put my Canadian Tire smart charger on the small battery. After a moment, after much clicking and whirring, the display went into a weird pattern I had never seen before. The documentation revealed that this was "reconditioning mode." Ah.

Low volts. BT charger protests. The CTC charger detects there's something wrong. Let's see if we can bring it back from the dead!