A quick story about an issue with a battery I ordered from eLearnAid, and their effort to fix the issue. Due to the usual sign of a bad battery - a drop in mpgs from the low 50's to the low 40's, plus knowing it was 4 1/2 years old (I've never had a lead-acid battery last more than 5 years in automotive service) - I ordered the drop-in replacement Optima the first week of December. It arrived near the end of that week. Due to the holiday rush I didn't get the chance to even open the box or install the battery until the weekend of the 22nd. Before I installed it I took a voltage measurement, unfortunately it read 10.5 volts. Far below what it should have been especially for an AGM lead-acid battery which has a very low self-discharge rate. However, I hoped for the best and put it on a smart charger overnight after installing it. The installation itself was painless, I ended up ignoring the detailed instructions they sent because I knew I could ignore half of the steps. It took me about a half-hour start to finish. The one recommendation I did use was to hook up a charger to the jumpstart terminal up front to maintain my settings. The next morning the charger said "bad battery". Not a good sign, but I reset it and let it go again. This time it completed normally. However, after a ton of driving before/during/after Christmas the mpgs dropped from the low 40's to the low 30's! And several at-rest voltage readings after sitting overnight showed me readings just above 11 volts over several days. The dome light was noticeably dim and yesterday it had an at-rest voltage of 9.9 volts. I'm amazed the computer allowed the car to start and didn't throw a dozen odd errors. eLearnAid immediately agreed to ship me a new battery. It arrived with a reading of 12.5 volts. I let it sit for two days and it still read 12.5 volts. I installed it this evening so I'll have to wait until tomorrow to see how the mpgs go, but I expect them to go back up where they belong. Moral of the story, don't even install a battery that doesn't arrive at full voltage, and eLearnAid will fix the problem if you get a dead battery.
Its good that you received a replacement without a problem, but pls note that 12.9V is deemed "fully-charged" for an AGM battery. So the replacement still was somewhat discharged.
All lead-acid battery chemistries will read between 12.6 and 12.8 when fully charged and fully rested (at least 3 hours without a load or charge). I've almost always seen a reading of 12.7 over the years. AGM batteries lose about 1% per month due to self-discharge so I would expect a reading slightly below 12.7 if it was manufactured a few months ago and has sat on a shelf since then.
My post #62 here: Replaced 12v battery with Optima | Page 4 | PriusChat documents my purchase of a GS Yuasa battery from my local Toyota dealer that had been sitting around for three months and yet measured 12.9V using my Fluke 87 DMM. That is not a one-time event; I bought another similar battery around a year later for my other Prius, which measured the same voltage out of the box.
