I don't trust any battery tester to give an accurate CCA remaining rating. The results can vary even wider depending on whether the place doing the testing can profit from selling you another battery, or profit by denying warranty claims.
I agree with fully charging your current battery. Most people act like the alternator is an instant magical battery charger but the fact is that it does a poor job returning a battery at 80% state of charge to 100%. Hours and hours of charging are needed to go from 80% to 100% no matter the charging source, and the closer the battery lives to 100%, the longer it should last.
So after any time playing the radio with the engine off or any other fairly significant battery depletion, the owner would be wise to use a plug in charger to bring the battery back to or near 100% and not just rely on the 'magical' alternator to do so, on their short trip to the store and back.
I've found some batteries that lived their whole life in the 85% range responded better, when discharged to ~ 50% then promptly recharged at a 25% rate of the 20 hour rate of amp hour capacity.
I am not a believer in the low and slow "trickle" mentality being best. I've taken Sg readings of such a charged battery and found them reading very low where as an automatic charger which holds mid 14's for several hours does much better.
Anyway Lead acid battery myths are likely to never die, as long as we use lead acid batteries.
In the OP's case, I would recommend doing a full charge monthly with a grid powered charger, and consider replacement come winter. At the minimum carry jumper cables, or a fully charged jumper pack when it does get cold again.
I have found my Northstar AGM battery to be impressive in terms of cranking power and voltage held under a longer slower discharge. But it is a very pricey and heavy battery and the extreme cranking power and higher voltage when discharging might not mean squat in the long run. Bragging rights only, perhaps.
Sears Platinum batteries are rebadged Odyssey batteries. They want huge recharging rates when deeply cycled. Just any plug in charger will not allow this battery to perform to its max potential, when cycled deeply. Users of these batteries, in deep cycle applications, need to be aware of this requirement and not just rely on reputation and a high price tag to reap the possible benefits of AGM over the much cheaper flooded starting battery options.
If an Odyssey battery owner every needs a jumpstart, they really need to find a charger that can feed a 100 amp hour battery 40 amps, until 14.7v is reached, then hold that 14.7v for 4 hours while the amps required to hold 14.7 taper toward zero. Not doing this, is dooming an expensive battery to an early demise, though it would likely still outlive a flooded battery given the same treatment.
