Probably New Auxiliary Battery Time

With the battery’s age and condition, it’s replacement time.

Check local-to-you automotive retailers, preferably their websites; they often have a function, you say you’re in need of a 12 volt battery, enter your vehicle’s stats, and it’ll show any they have that are compatible.

If websites fall short, just phone retailers, describe your vehicle and tell them you need a battery.

 

No, the Prius has 2 batteries. The 12v auxiliary battery, and the hybrid battery. The 12v battery in a Gen 2 Prius merely powers up the 12v auxiliaries, like computers and lights. The Hybrid battery does all the engine starting and AC operation.

 

A hybrid like a Prius is not the same as a "normal" car with start-stop function.

The 12V in a Prius only powers up the computers- takes under 30 amps for a couple seconds until the HV battery takes over via the DC-DC converter. Very light duty.

Start-stop "main" battery has to run the starter motor- maybe 150-200 amps for a second or so. If there is an "auxiliary"battery, it has to power all 12V loads while the engine is off.

I have had good results with Toyota 12V; also Napa AGM or Deka (made by East Penn manufacturing).

Posted via the PriusChat mobile app.

 

Once the car is "ready" the HV system moves the car and starts-stops the ICE, it also powers the DC-DC converter which charges the 12V battery and all 12V loads.

The diag screen on the MFD isn't a good substitute for a decent multimeter. A fully charged AGM 12V reads about 12.6-22.8V with the car turned off. When "ready" the DC-DC supplies "about" 14.0V steady under most conditions.
Posted via the PriusChat mobile app.

 

Yeah that voltage doesn’t mean much. Try checking voltage first thing in the morning, car off, with a multimeter.

voltage is just tip-of-the-iceberg for battery testing, but still good for a quick check.

 

replace it before you get stranded somewhere

 

Might be slightly higher at posts, but jump point more convenient.

 

how long had the car been off when you took the reading?

12v is low, but not totally unacceptable. the more important reading is with a load, high beams, radip fan high, etc.

 

That is good advice from bisco about doing a load test. in addition, the resting voltage needs to be taken after the battery was fully charged (which could take 16-18 hours housing an external multi-step automatic battery charger) otherwise it does not mean so much.

In the load test mentioned by bisco, if the voltage is above 10.5 V then it is not so much an issue to the car, but it does indicate a severely compromised battery which you should consider changing. Personally, I wouldn't think twice about changing the battery if, in that load test, it showed a voltage below 11 V.

Good luck.

PS, if you want to charge the 12 V battery using the car, it would take a similar amount of time with the car on in READY to fully charge and there would be no difference driving around or not.

 

They are probably right, given they have probably got some commercial beast that can be set to charge at 10 or 15 A.

I can vouch for the adequacy of the C-Tek MXS 5 as that's what I have and have been using for some years quite successfully.

 

I acquired a Solar BA5 maybe a decade back; current similar tester is BA9. I’m not that knowledgeable about how it works, but it seems to do well. You enter some stats about the battery, do the test, and it gives you as-tested CCA and a verdict: pass, pass-but-needs-charge, or fail.

I’m using essentially the same charger I think, model 4.3. Our car use is about as low as you can go and still justify ownership, about 3k kms a year. I keep the battery on the charger pretty much constantly; car often sits for multiple days. For convenience I have the quick-connect wiring installed. Current battery was installed September of 2015, still showing like-new readings.