I have 2 group 27 deepcycle batteries I took in for testing. @ 2 places. Continental brand batteries.

1st place input 450 CCA in the tester, both batteries tested good. ( I thought the 450 was to low of input, hense shop #2)

2nd place used 575 CCA input, now both checked bad. So I'm thinking both may be border line.
I mentioned the previous shop test, so they rechecked. Now 1 was good. Then they rechecked at 450, both good.

Do I have no bad battery, 1 bad battery, 2 bad batteries, or 2 unqualified shops?

i always replace questionable batteries, it would suck to miss a weekend of boating over a lame battery

I think your right, they are borderline at best. If there remaining capacity is about 400-450 CCA, they will test good if tested as a 450 CCA battery, and bad if they are tested as a 575 CCA battery. Either way the batteries are weak and will fade fast at this point.

Merc recommends minimum 750CCA for a 502Mag MPI.

Dave

Thanks for reaffirming my thoughts Dave. Just wasn't sure if that's how they work, good at the lower rating, but bad at the higher.

junk them, the last thing u need is a battery problem -trust me.

The last thing you need is a blown engine and drive.

Bad battery would be at the top of my list of desired problems actually!

But in all seriousness, I agree that these sound like they are fading.

i'm w/you fund razor, bad batteries are at the top of my list for desirable mechanical problems -jeff

Update

charged both batteries for 2 days each @ 2 amps, and retested at 1st store, but had them use 700CCA. 1 Battery good, other required recharge and retest. I don't think so Tim, it was charged. So replaced it with a dual purpose battery with 1000CCA from AutoZone. Duracel (AutoZone) DieHards and many other are all made by the same maker: Johnson Controls. I 'think' JC also makes the Optimas????
If the other battery acts up this summer, I'll replace it with a starting battery.