How did I kill my 2020 Sequoia TRD PRO battery?

Had the travel trailer (TT) plugged into home outlet, pre-cooled the 3-way refrigerator on AUTO AC. A TT 12v battery minder in cigarette lighter outlet showed 13.6v on the TT battery. Yesterday , about 10 hours before the trip, connected the Toyota 7-pin to the TT, left TT plugged into home outlet. This morning took off for a 6-hour drive, stopped for gas and a pee break, everything was great…until we drove into the campground. After I paid the owner for a week’s-worth of tranquility, the TV wouldn’t start: no lights, nothing ; while waiting for theAAA I did go into the TT and the 12v minder was reading about 8v. AAA came out here, boosted the battery, the TV started right away , I ran the engine for 30 minutes disconnected from the TT; shut down the engine, tried to restart the TV with no success, not even a feeble crank; the battery is completely dead in the TV.
A thoughtful campground neighbor gave me a trickle charger, which doesn’t seem to do much, so I figure the new TV battery is needed. AAA won’t have any providers with a new battery till tomorrow morning, so meanwhile I’m trying to figure out what I did to kill the battery; it’s 4.5 years old and has 40k miles.
After I plugged TT into a 15 amp pedestal, the TT 12v battery minder now reads 13.67v, the fridge(which was off when we pulled into our spot) is happily chugging a/c. I don’t have the multimeter with me.
I wonder what I did to kill the Toyota battery. As I imagine, it was supplying the TT battery via a 7-pin connection, but not recharging and went dead beyond resuscitation?

 

It’s 4.5 years old. Average life expectancy of a battery these days.

 

I think you are right. I just went to take a look at it and noted a rotten egg smell and bubbling noise. It’s cooked. 40k miles doesn’t seem like a lot for a battery, but I guess it was time to go. I’m rather miffed now at the dealership that sold me the car last August and not installed a new battery; it’s a Toyota dealer; the car is Toyota-certified for one year. I wonder if that includes the battery…the manufacture date on it is 2019.

Now we are in rural down east Maine; hopefully AAA will bring the new battery to the campground; if not,I’ll have to somehow hitch my way to the local NAPA store and back to procure the battery on me own.

 

Can you rob your camper battery for the trip to the store for a new truck battery?

 

Batteries aren't affected by mileage. The environment plays a really big part though, extreme heat and cold are tough on them. They can even fail spontaneously. At that age, your battery has lived it's typical expected life span.

 

4.5 is great. These days if I can get 3years out of one, i'm ready to swap it out early to ensure I always have juice.