Battery question

[Trav]

2013 Altima.
Battery, Group 35 EverMaxx dated 4/2017 and installed shortly thereafter.

Never had a slow crank issue. Occasionally hooked up to BT Jr. 750mah tender.

Woke up the other day to no puddle light and only the push to start light and the security light would work. Then I heard a continuous click click click click.

Multimeter said battery was 5.4 volts!

Pulled it out and tested and it was 6v. Is that much difference normal?

I then installed an Interstate MTX35 AGM battery. Tested 13.1v before install. Once terminals hooked up it was 12.7v.

Normal or too much of a drop? No aftermarket devices hooked up.

Went back to interstate and he hooked up a digital meter to the battery to allegedly test the alternator. Said it was fine.

5 years on a Wally world battery is fantastic, I have got 5 months or less out of them more than once. No more and now the real Die Hard is gone I buy Napa Legend made by East Penn who made many of the original Die Hards and Deka.