Tested it how? With a carbon pile load tester or something else?
a tester that simulates a cranking/starting load (about 150-250 amps) is the only way to ACCURATELY test a battery.
" 12.8 volts - it's good! " .... really means nothing at all when the battery isn't under a working load.
I have one of these: Sun VAT-40
Old school is still good school. Or the nearly similar Snap On MT552 (which now owns Sun), Typical selling price is about $150 without cart. Be sure it has the inductive pick up - green cable. Test battery, alternator, and starter with a real test, ON THE CAR .,,,,,,,,,,, very quickly.
Lots of good videos on You Tube on these.
"Computer Test" is nearly always junk test.
There are good modern ones but seldom used by selling stores ($$$$).
Even a group 35 Northstar battery has way more CCA 740 vs a typical group 35 with typically at most 640 CCA and many group 35 have only 550... Group 24 is typically around 700 CCA but other group sizes can easily be the same has well.
I thought that the Northstar is one of the better batteries, together with the Odyssey (it's made by them I believe) you make it sound as though it's middle of the road, what gives?
Ahh you are very correct... The Northstar battery is a great battery. I meant to show that for the same size the Northstar battery had way more CCA. And it weighs a lot more too... A group 35 Northstar weighs 46 lbs... Regular top of the line flooded battery weighs 37 lbs. Big big difference. Better battery Northstar.
Okay I took my ticket with me to an Advance Auto. The Walmart tech set the CCA on the Midtronics tester to 100 CCA for the battery that is rated for 700 CCA. It's a 26F. Hence it checked out at 85 CCA and passed.
Guy at Advance has same tester punched in 700 CCA and ran test. It shoed "bad battery."
Went back to Walmart. The auto area was closed this Sunday. They said I have to come back in Monday. I demanded a manager. Showed him the ticket where his guy committed fraud to not warrant the battery. He said he can't do battery warranties but can refund the battery to a gift card the full price on the receipt and that a new one is on sale for $3 less for Veterans Day sale anyway...
I ended up returning the bad one and buying a new one... Did it in two separate transactions, so I certainly restarted th three year warranty. Took the new one to Advance to have it retested...
Guy said it tests at 815 CCA. Brought it home, and it turns the car over and starts it like you wouldn't believe.