My battery failed after 3 years. My 2015 was delivered 87 days after its manufacture date, assuming GM-provided information is correct. For 35 of those days the car was on the ship. Granted that the battery was in "transport mode" for much of that time. The problem is that my car is not driven much, and that the rest load is somewhat higher than other cars (presumably to accommodate the remote key fob). Lead acid batteries experience both self-discharge and sulfation. Sulfation is the formation of lead sulfate on the negative plates, which increasingly occurs when the car is not driven much. In my case once every week or once in two weeks. The lead sulfate is initially in the form of small particles, but with time forms into a more solid plating which prevents lead ions from participating in the recharge process. The result is diminished storage capacity and reduced voltage at "full" charge. I had been recharging the original battery at some, probably too long intervals.
Since the failure occurred at an inconvenient time, I set aside my prior resolution to never purchase another parts store battery and did so again. This battery lasted little more than a year, at which time it was replaced by a store warranty replacement of the same battery. I have been more diligent in periodically recharging this battery than previously, but the COVID pandemic has had me driving the car even less. The result is the parts store battery is failing again, down to 11.4 volts at "full" charge. The car still starts, but is not happy about it and the battery is being recharged every 4 weeks.
At this point I have decided that a change in chemistry is required. I have had good luck with my motorcycles switching to LiFePO4 batteries (Shorai brand). Lithium Iron Phosphate does not sulfate (obviously), and self-discharge is much less. The battery is still vulnerable to over-discharge due to rest electrical load - which is not zero on modern motorcycles. Some diligence is needed to keep these batteries sufficiently charged, since once voltage gets below about 9.5 volts the battery becomes a brick. I recently became aware of Antigravity batteries, a company that sells LiFePO4 batteries in car sizes, including our H6 size. This company started out in motorcycle-sized batteries, followed by race car batteries featuring large weight reductions. Porsche owners are big fans, as the GT3 cars are also not driven much. Antigravity has now incorporated features that should make LiFePO4 batteries more idiot proof: an internal switch disconnects the battery if rest voltage falls below 11.5 V (full charge is 14.2 V), with a fob that re-connects the battery for "one more start". There is also a condition monitor that works with a smart phone app to communicate information such as state of charge, with an alert when the battery needs re-charging. Various capacities are offered from 20 Ah to 60 Ah; the smaller numbers for racers who want the lightest battery and the higher numbers for those who want the longest inactive duration. I have ordered one of these batteries but not installed it yet. I will provide a use report when I have some experience. Drawbacks are (1) little actual field experience; (2) fairly pricey; and (3) 100% made in China.
