Is there a TSB they can reference that recommends an AGM battery? Otherwise, the best everyday price is $170 (3yr warranty)on the Duracell from Sams Club. Next up, pep boys has the bosch 65-AGM for $140 (4yr warranty) with $60 online coupon code. Next up, Sears has the diehard AGMs on sale for decent prices right now. Otherwise, there's always independant battery shops that are worth checking out.
I assume they would recommend an AGM for faster charging ability - The smart/regenerative charging system is the dumbest thing manufacturers have come out with. I don't understand what was wrong with just regulating to 13.4-14.8V depending on temperature. For that matter, a straight 14.4V would serve just fine. The most a battery is taking in charge is going to be 25-30 amps. At 14V, thats just about 425W or about .5-.6HP - not a significant load. I'd like to see what the actual MPG gain is of the system in comparison to old-style dumb charging.
FWIW, handheld electronic load testers give a pretty decent picture of cranking amps and health - especially when testing in a vehicle and you can do a crank-voltage test (how low the voltage dips while turning over the car). Otherwise, the best test to do is a full true carbon-pile load test at 50% of the battery's rated cranking amps. An 800-1000A load tester serves well for this purpose. I use and recommend Autometer brand. For a handheld tester, I use both mid-tronics and argus brands and both are extremely accurate for cranking amps, but can't put an extended load on the battery to weed out a weak cell.
