I have more battery chargers and maintainers than I know what to do with, so this one is getting Marie Kondo'd.  Works perfectly.  The last two photos show it charging (red light) and switching to 'float' mode (flashing green light) on an old car battery that I have laying around.

From the original Deltran website:
The Battery Tender PLUS!

The Battery Tender PLUS is a 1.25 amp battery charger designed to fully charge a battery and maintain it at proper storage voltage without the damaging effects caused by trickle chargers. Included is a quick connect harness for hard to reach areas.