The other day, I went down to start the car. I first disconnected the battery tender. The connection plug was super hot. Almost burned my fingers. Never had that happen before. So I drove off and everything was fine. The next morning I went to start the car and it was dead. I had to use the key to open the trunk and hook up a charger. Got it fully charged, then hooked up the battery tender. The next morning, the tender said fully charged. I unplugged it, started the car and got the low battery warning. Anybody have an idea what's going on here? Could the tender be the problem? Battery is a Die Hard AGM and is only six months old. Stumped.

 

The connector COULD be hot because the tender was DRAINING the battery due to a short or something. That would explain at least a bit of your problem.
Yeah, I'd replace the tender and all associated leads/wires.

 

the low battery warning are cached in touch screen module and do not go away even with a fully charged battery. make sure its still fully charged and lock the car and let sit locked at least 15 minutes iirc and this clears the messages out

 

Chazaroo,
What is the BRAND and MODEL your battery maintainer, and when and where did you buy it?

 

Whatever you have it's clearly rubbish.

Get a CTEK charger and superior European technology will see you good for many years...well it has me for over 18yrs without issue (cepting when I ran over one!)

 

Had the battery (DieHard AGM) checked today and seemed fine Voltage 13.02 Measured 902 CCA Rated 900 CCA, Temp 100. So I think it has to be the tender. It's a: Battery Extender powered by Schumacher. I got it at a tool store in Vero Beach. I think I'll just toss it and get a new one. CTEK 3300?

 

Just ordered the CTEK 3300.It arrives next Tuesday.

 

You are lucky the car did not burn down to the ground, which is what happened to a forum member here.
Couple of things:
Find an excuse to have that battery replaced, its life has been significantly shortened.
Make double sure that you have an AGM battery and AGM mode enabled.