Discharged 12V Battery

One nice thing about the Prius is that, after a jump start, recharging the battery doesn't really require driving around like your granddad's car did. The Prius 12 volt battery is getting charged at the same rate any time the car is in READY, whether you're driving around, idling, or just sitting there in READY with the engine stopped.

-Chap

 

You know what you need for Christmas, or Boxing Day...

 

There's likely both in your near future, but yeah: charger, a 4~5 amp smart charger. Hook them up and right from the get-go they assess and should determine if the battery's even viable. If yes, it goes into a multi-stage charging regimen, will automatically taper off at the end, and can be left on indefinitely, if you need, say for an idle car.

 

I believe this is Mendel's preferred charger, ATM.

http://www.amazon.com/CTEK-56-864-Automatic-Battery-Charger/dp/B006G14FK8

 

Ours spends half it's life on that pictured charger, but we're very low usage, and I'm obsessive...


(right now)

 

I believe your understanding of percentage SoC as it related to voltage may be a bit off. This chart gives an idea:

The top line relates to advanced Lead/Acid chemistry such as the AGM used in the Prius (if it is original equipment). The bottom line more closely resembles regular flooded lead/Acid, which is probably for what your charger is designed. For a Prius battery, you can see from this that 0% is ~11.6 V; 50% is 12.35 V; 75% is 12.7 V; and 100% 13.2 V. In relation to your charger 75% would be ~12.38 V and 100% would be ~12.8 V. In order to raise the voltage to 100% potential, the charger has to use a voltage higher than 100%, typically 14.0 - 14.4 V (depending on type of battery), so when a battery is just taken off the charger it has a voltage that is more than 100%. This is called surface charge and will dissipate over about 2 hours to the natural full state voltage of which the battery is capable. On a good battery you would want to see in the region of 12.9 or better.

If your battery is truly only showing 12 V after reaching 100% charge, then either the charger is faulty or your battery is. If it truly was 9 V when you started, your battery is toast and you are on borrowed time. A voltmeter across the battery would eliminate the need for guessing.

That depends on you pattern of use of the Prius. If it sits for days without use, it would be diligent to use a maintenance charger all the time the car is not in use. With a "quick connect pigtail" installed it takes only a few seconds to connect/disconnect the charger.

Anyway, I provide the above for your information, your millage may vary.

 

lol

 

Still with the "ho-hum" charger?

First step would be to assess it's viability, either DIY with something like Solar BA5, or remove it from the car and run it down to an automotive retailer (Pep Boys for example), and have them test it.

Or: how old is it now? If it's getting on, maybe just go directly to replacement?

 

No sorry, I was thinking of the battery.

Do you at least have a digital multimeter? See what the voltage is reading? It might be artifically high, raised by the charging. The expression is "surface charge". Turning on the headlights for a couple of minutes will help to clear that, pull the battery back to realistic voltage.

I know I'm harping, but you need:

1. A smart charger, 4 amp range, one that assesses the battery when you hook it up, will actually "bail" if it's a lost cause. If it's ok with the battery, it'll then proceed into a charging session, going through various stages.

2. At the least a voltmeter, so you can get some idea where you battery's at. Or much better, an electronic load tester, say Solar BA5 or similar. Barring that, get the battery to either a dealership (the visit will likely cost) or an automotive retailer selling batteries. Nowadays they should have a pro-level equivalent of the BA5, but you'd want to phone and check. It's good policy for them to have such a tester: it allows them to demonstrate the condition of your battery, AND the batteries they're selling.

Really not sure, but an ailing battery is known to cause odd behaviours in the car.