A PSA for Gen 2 Prius Owners...

Depending on where you bought the battery and if you have the receipt they'll likely swap it out or charge it up... But especially because it's your home and you'll be using 12v when car is off ---> go to a Harbor Freight and spend $5 on a trickle charger to keep 12v battery fully charged whenever you're close to a place to plug in.

 

Not trying to be a charger snob, but I would go upmarket a bit, get a smart charger in the $50~80 range. Something that will go through a charging regimen, and can be left on indefinitely if need be. IIRC the Owner's Manual sets the 2nd gen ceiling around 3.5 amps for charger capacity.

CTEK Multi US 3300 would be my pick. That model's been around for quite a while, might be superceded, but a good line to check out, see what they have around 3.5 amps now.

 

With our OEM Yuasa, I had a senior moment, left one door open, noticed about 18 hours later, and it was down to about 11.9. That I considered near-death. Yeah a 100% AGM, without a temporary "surface charge", should be reading around 12.75 to 12.90. One that's 4~5 years old but well maintained, around 12.6.

A battery that's been sitting on a shelf for 10~12 months might be reading 12.5, 12.4 at the worst. It's a long sit, but it's isolated, not subject to a slight but steady drain, like an installed car battery. If an electronic load test is done on such a battery, and it's viable, you'll still be seeing the CCA well above spec, and the verdict is "good but charge", something like that.

Look into the Solar testers if you're interested. I have a Solar BA5, but I think the current Prosumer best choice is BA9.

 

The resting voltage was too low(11.5V). I can only imagine that it sat on a warehouse shelf for months.

You'd think driving would charge it up but the Gen 2 charging system is slow. Had to get it properly topped off at O Reillys. It's been fine for over a year since.

 

12.4 volts right after extended run is still pretty lacklustre, likely partially surface charge.

Check in your area for automotive retailers that can test that battery, with an electronic load tester. Retailers will typically do it for free. See where you stand with that. Most of the testers require entry of the battery's spec'd CCA, plus what type it is, ie: AGM rectangular, AGM cylindrical, or conventional flooded cell. With that it will test, give a verdict, and display as-measured CCA. A brand new battery should definitely show well above spec'd CCA.

If it does not indicate CCA, probably about 325, close enough for the test anyway.

The pro-level testers usually can do a print-out as well. If it fails, I would take the print out back to the seller. They could very well have a shelf of very stale batteries. Maybe not, trust-but-verify.

This chart is for conventional 12 volt batteries. AGM's should be about 0.2 volts more:



Sorry if it seems like I'm dogging you here, but it really seems like very stale stock. Hope I'm wrong, but an electronic load test would dispel the uncertainty.

 

I'd hardly consider 65 mins an extended run, considering it would take 16 to 20 hours to charge that battery in-car.

Get your battery on your new charger for 24 hours and then get back to us with your results.

 

After charging, drive the car a few days, and then check the voltage first thing in the morning. A battery fresh off the charger can show high voltage, but it's what they call surface charge.

 

Yea, I agree that my Harbor Freight charger is a bit of a joke in terms of quality & price... And yes, I've noticed often its inability to do as much as I want it to... But in this case, this person is living in their car, so I highly doubt they're going to have a spare $50-80 in disposable income.

 

I was just going to say that a good 12v battery should be between 12.6-12.8v
Here is a link to a 4amp charger/battery conditioner that could bring it back up to where the battery needs to be at.
4 Amp Fully Automatic Microprocessor Controlled Battery Charger/Maintainer

 

That's slightly over the second gen amp ceiling for charging (3.5) but maybe ok, close.

 

If the aim is to ascertain the current status (no pun intended) of the 12 V battery, this is very bad advice. Driving for a couple of days could introduce any number of unknown variables.

While Mendel is correct to point out surface voltage and the fact that one should never measure a battery's voltage immediately after removing a charger, there are at least two ways to deal with surface voltage.

• Apply a current load for 20-30 seconds then remove. Let the battery sit for 5 minutes to allow the voltage to settle back to its resting voltage.
• Wait for 2 hours after removing the charger so the surface voltage can dissipate.

I don't think 0.5 Amps between friends will make any significant difference. What I think the warning is really about is cautioning owners against using a high (~16 A) current charger which will introduce the possibility of off-gassing or other dangers, such as exploding, if the battery is in poor condition.

While this may be true of standard flooded Lead/Acid batteries, an AGM normal range would be 12.9 - 13.2 V. The charger you use should have a setting (or auto-detect feature) to use a different charging profile for AGM and Gel batteries versus standard batteries. On the AGM setting, the trickle charge voltage will be 13.2 V and the charging voltage will be ~14.7 V.

 

Try Napa they sold me a car battery that worked just fine.