Duracell 12v "Prius" battery

Does anyone have experience with the Duracell branded AGM 51P 12v “Prius” battery previously mentioned on Priuschat by Rude person's? jdenenberg, in response to one of Rude person's’s mentions, asked if it had a vent port, but never received a response.


This is why I ask: Yesterday ( after my “parking lock malfunction” experience Boxing Day evening, and subsequent discovery of this invaluable website), I called the local Batteries Plus store to ask if the Duracell was in stock. The gentlemanly franchise owner told me it was. I asked “is it vented?”. He told me “No, it is completely sealed; no vent”. Having no EE nor automotive smarts, I didn’t question him further.


But after hanging up, I went online to see what the Duracell car battery website said about the battery. ( Priuschat won't let me create links or use any phrases vaguely resembling links until tomorrow - I just joined today). There, I found the following descriptors/statements for the AGM51P: " flush manifold vented cover” and “Battery gasses need to be vented to outside: AGM valve regulated battery required. Battery located in trunk.” The AGM51P is listed as the "AGM51P Prius battery" at their website.


I have not called the store back. Can anyone confirm this battery vents to the outside through a vent tube, just like the OEM on my 2010 (in service from 8/09, courtesy of “Cash for Clunkers”)?


Two nights ago, after the problem arose, and after perusing this site, I borrowed my neighbor’s multimeter. The battery was the problem. I measured 9.7v at the terminals. Got the car to start by the “accessory mode/push and hold power switch” method. Drove it about 8 miles, then back into the garage, and turned it off. Measured 12.54v immediately afterwards. It has sat unused since. Haven’t activated any lights. Garage temp probably mid/upper 40s (F). Measured 12.29v the next (yesterday) morning, the same 12.29v that afternoon, and 12.23v this morning. All at the terminals. No load testing attempts.


Awaiting arrival of Battery Tender Jr. from UPS. Plan to fully charge (or TRY to fully charge) the OEM, then monitor it - based on my reading of threads here. And then decide if replacement warranted.


OR, am I wasting my time – should I just replace the OEM now? For many months now, mainly short (6 miles or so roundtrip) trips once every 3 or 4 days. AND, 1 episode of interior lights accidently remaining on for 36 hrs. – about 3 weeks ago. No start problem was noticed at that time.


I ask about the Duracell (East Penn, as the Duracell site indicates) because the price seems right for a non- DIYer. $179 installed, w/48 month full replacement “nationwide” warranty. But jdenenberg had several good points/questions.

 

Yes, I have (if I replace now). I've read many of the threads here.

 

Do you judge the battery to be marginal because of the rate of decline in voltage I described above (once it was up to 12.54v immediately after driving it 8 miles)? One new data point - new voltage now, 16 hrs. after the (last) 12.23v, is 12.18v. Car remaining at rest.

Or is it marginal because 8 miles of driving "only" boosted voltage from 9.7 to 12.54v 2 nights ago? Or because voltage was first measured at such a lowly 9.7v after trying, unsuccessfully, to start car after it had sat for a few days (about 3 weeks after interior lights accidently remained on for 36 hrs)?

If I did replace the battery, would the short trips I described (above) now keep the new battery charged (w/o additional measures, such as battery tender/minder)?

 

Thank you, all.

I would still like to hear the reasoning leading to the determination that my battery is marginal, or toast. So I can learn something.

Looking for the kind of explanation typically provided by posters like jdenenberg, doruron, Patrick Wong, and Bill Norton (to name just a few).

And still hoping to hear about the Duracell. edthefox5 mentioned the Optima is cheaper, at Advance Auto - $169 online pickup at store. Is that cheaper than Duracell $179 installed (for the non-DIYer)?

Just for clarification, did Den49 mean to answer "No" (rather than the "Yes" posted above)?

 

Thank you.
Just to be clear, the 9.7v reading occurred 2 days before my first post here. I realize my opening post could have been clearer.

1. No problems before Dec 2014. Car use once every 3 to 4 days, 6 or so miles roundtrip. Near end of first week in December: interior lights left on for 36 hours. When discovered, car started up fine. No investigation done.

2.Dec. 26 evening: try to start up car for first time in 3 days. Get "parking lock malfunction" warning; car won't start. I find Priuschat, and read about it. Borrow a multimeter (never used one before). Measure 9.7 at posts. Car starts using "emergency start fuction" described in manual. Go for 8 mile drive. Park in garage; measure 12.54v right after turning it off.

3. Dec. 27 morning: measure 12.29v. Car continues to sit unused.

4. Dec 28 morning: measure 12.23v. Car sits unused.

5. Dec. 29: (these are new measurements - the last 24 hours - I'm first reporting now): Measure 12.01v in morning. Use car; travel 4 miles roundtrip, with 1 hr. stop halfway through. Immediately at end of roundtrip, measure 12.64v. 30 minutes later: 12.32v.

JC91006, do you judge the battery to be unhealthy because my 9.7v measurement was a SIGNAL that it is unhealthy (ie: a HEALTHY battery subjected to the same temporal sequence of "interior lights left on" stress, and previous/subsequent low car use pattern, would NOT have declined to 9.7v on Dec 26 evening, after attempting to start the car)? Or, are you saying that battery discharge down to 9.7v CAUSES an unhealthy state from which it cannot recover?

I now realize the timeline in my opening post was presented in a very convoluted manner.