BatteryMINDer Plus $19.99 (Cyber Mon Sale) @NorthernTool.com

I have only one and have switched it around for years to maintain our home's backup generator battery, our boat's battery, and most recently for several years to maintain are RV's engine battery 24/7 while the RV is parked in our back yard. I plug the BatteryMINDer's input into an RV 120V receptacle and it's output into a 12V always-hot receptacle on the cab's dash. The RV itself is plugged into a 120V receptacle on the side of the house 24/7.

I just ordered another one at that great price through the link that otrfun provided above .... thanks otrfun! I paid way more than that way back when for my first one.

Sometimes this "black Friday"/"cyber Monday" stuff is more than just hoopla ... I just today also ordered a new SOTA flat screen TV at a bargain basement cyber Monday price.