I grabbed one from my Kress 20V batteries off the shelf and put it on the charger, only to see a solid red LED light up and stay there. There was no blinking or charging, simply solid red light that shows that the charger believes the battery is dying. There must be a way to revive it to not waste the battery.
I checked the voltage display on the side and found that it stay almost at zero. The charger simply refuses to even start the charging cycle when the voltage of the battery is below a certain limit, and that causes that solid red light. At first it did not make sense, but in the end the solution was to use another working Kress battery to jump-start the dead one.
I took a second Kress 20V battery that still had some charge, and laid both on the table. I checked the top of every battery, where they connect to tools and chargers.
Reviving a Kress 20V Battery with a Solid Red Charger Light
There was a little plus symbol on the casing, which marks the positive terminal. The negative terminal was on the opposite side. It was quite simple.
When both batteries were marked, the next step was to connect wires between same terminals, to move voltage from the good to the dead. I used flexible wires with ring ends for safe connection.
Then I tied the negative wire the same way, from the negative terminal of the good battery to that of the dead.
I kept the ring end flat against the contact point on the battery, while the voltage transferred. The wires were pretty thin, so I certainly risked that they heat up, if something would fail. The goal was to move only the needed current and voltage into the dead battery, to raise it above the minimum limit that the charger requires to recognize it.
I left the batteries connected for around fifteen seconds, watching the wires closely to make sure that nothing starts to smoke or melt. After that I removed the wires, while I watched the stop watch.
I removed the wires carefully, then put the dead battery aside. I brought the battery to the charger and charge it, curious if the solid red light will return. This time, instead of staying red, the LED blinked green.
Blinking green light showed that the charger knows the battery and started the usual charging process.
The solid red error light was no longer there; everything returned to normal charging. The battery revived from what seemed like hopeless failure, thanks to the quick fix.
