Another battery question

[Glamper64]

I took my battery home and put it on my Tender which usually charges it for a day with the red light on, then the light goes green to Tend mode all winter. I'm not sure how old this battery is, probably original from 2017. After a week the red light is still on so I leave for another week. After about three weeks it starts flashing red and green signaling an issue. I disconnected it from the Tender and tested it...8.3 was the reading...battery charging issue? I should mention that after a week I added some distilled water.
Question, since my RV is permanently hooked up to shore power for the season, is this old battery okay to use...I've read that I don't even need a battery when plugged into shore power because the converter takes over the batteries job? I would need a battery for power outages so I should have one. Also the battery display read full in the RV all last season.
Questions, should I just buy a new RV deep cycle battery?
Does an RV need a good fully charged battery to operate properly when plugged into shore power?
Thanks for any help.

[TaftCoach]

Bless that battery, it has served you well for longer than expected. It has died. While not quite flat lining at 8.3 it won't be recovering too anything near it's former greatness.

Depending on how long potential outages might be, and how much you rely on the battery in those situations a cheap lead acid will work for you just fine.

[TaftCoach]

The display read full because you had power running to the battery. Unless you invested in a meter with a shunt that meter just measured the current at the terminals. If you unplug it will be slightly more accurate. Unplug and monitor it for a couple hours and you will know even more. Likely you were well under 12v on that battery for a while.

You could take it to a auto parts shop for a battery test.

[Seann45]

Your battery is toast... buy a new one. the thing everyone forgets about is that if the trailer becomes detached from the tow vehicle you need the safety brake cable to engage and if you have a dead battery this will not happen. How distressing would it be to see your camper pass you on the highway?

[Glamper64]

Yes I thought so thanks.
I'll give it a proper goodbye

[RogerR]

Since your RV is hooked up for the season the only required use is to operate the emergency brake. But another use for the battery is to power your RV when the electricity goes out. Lots of campground outages in my area so that is very handy.