12 volt Battery Status Indicator on Gen 2

There sure is Entering Maintenance Mode (aka 12V Battery Check) without Switching Headlights ON/OFF | PriusChat

 

Run the test after the Prius has set overnight before you drive it.

Need the three values

Accessory Mode:
Ignition On Mode:
Ready Mode:

Here is a chart that you can relate to concerning voltages on a AGM type battery. FWIW, yours sounds a little weak to me. Will know more once we see all three figures.

 

I would not describe the 12 volt battery readout on the MFD as precision.
On test I have carried out on a number of gen2's the display has been as much as 0.5 volts out against a calibrated DVM, and in every case under reads the actual voltage.
My suggestion is you measure the voltage at the battery while also using the MFD. This way you can see what the error is if any and then apply the offset to any further reading using the MFD.

John (Britprius)

 

I do agree with John about the MFD not being a precise instrument. If you don't want to pull out the back panels to get to the battery post, you can check the voltage at the jump post in the main fuse panel under the hood. Generally speaking, there is usually about a .2 volt drop in measurement from the battery posts versus the jump point. I believe that is due to resistance. You may find less or no drop whatsoever.

 

That battery is dead. Get a new one. Look at the chart I posted above.

A new fully charged AGM type battery should read the following when running the test.

Accessory Mode: 12.6 volts or higher
Ignition On Mode: 12.4 volts or higher
Ready Mode: 13.8 to 14.2 volts

 

Those voltages are very low and indicate an immediate replacement of the battery is required.
When the new battery is bought check it's voltage before fitting. This for a fresh fully charged battery should be 12.8 to 13.0 volts or may be a little higher. If lower than 12.8 volts charge before fitting.
I would not accept a battery with a voltage below 12.2 volts as partial discharged batteries sitting on a shelf sulfate the internals quickly leading to a shorter life and capacity.
Can you give some guide to your location in your avatar as we would then be able to guide you to suitable replacement batteries.
As Dorunron pointed out above the voltage drop shown at the jump point of 0.2 volts may not sound much, but when measuring the voltage of a lead acid battery that sort of discrepancy is very significant on it's level of charge.

John (Britprius

 

As John said above, don't accept a battery that is not fully charged. 13.8 volts is a little high though, I think he mistyped that one, probably should read 12.8 volts. Same for 13.2, probably meant 12.2 (discharged and sulfated).

It is important that a new battery is fully charged BEFORE you install it in the Prius. The charging system is not very robust.

Use a digital voltage meter. Measure the voltage at the posts BEFORE you install it. If it reads less than 12.8 volts, it is NOT fully charged.

 

Thanks Dorunron yes miss typed, and now corrected thanks.

John (Britprius)

 

The Optima is way over priced and with a comparatively short guarantee. Bosh, Varta, Exide all make direct fit batteries from around £45 with up to 5 year guarantee. I think you will find the OEM battery is about £90. Do not go to Hal--rds they are expensive and don't even list the correct battery. I will post more details a little later. I have a post on here detailing how to fit a high capacity mobility battery if you are up for only minor DIY.

John (Britprius)

 

When buying a Prius battery the things to look out for are:-
It has an external vent
The terminals are the small JAP terminals not the larger standard imperial.
When the terminals are closest to you the positive (+/red) terminal is on the left. Many batteries advertised are not being the other way round.
Examples of the correct batteries from Ebay.
Item no:- 350869455183, 370570483080.
These batteries should be available at your local motorist shop and there are others such as Lucas. If you pay a little more you can get 5 year guarantee versions.
If you need any more help just ask.

John (Bitprius)

 

Hmmm, I just checked my battery with a DVM and read 12.02V, it's the original 2006 battery the car was off over night, going by that chart I'm probably in need of a battery change?

I tested it out of curiousity seeing as there was a post about the MFD acting strange when your battery is going dead, not registering touches, sometimes registering touches at the wrong location (try to turn on environmental controls is pure madness sometimes). Now my battery may be low AND my MFD is busted, but I'm curious if I should replace the battery first then see if that affects the MFD usage.

 

Definitely replace the battery first, see if that's causing your MFD to act crazy. if not, at least you won't have to worry about being stuck somewhere in need of a jump.

HTC Evo 3D

 

Mike I do not like to be the bearer of bad news, but I doubt very much the low battery is causing your MFD problems. Once the car is made ready the voltage will be at around 14 volts and the 12 volt battery can actually be removed and the car will still operate normally.
I agree your battery is at the point of expiring and is due for replacement.

John (Britprius)