12 Volt battery operation range?

[Cacti]

My scan guage normally reads 13.9 volts regarding the 12 volt battery while I'm driving, yesterday while driving it read 13.3 volts, what is the normal operating range? Should I be concerned with the 13.3 volt reading? My Prius is a 2007, purchased new July 2007.

Poleikleng

[jdenenberg]

Originally Posted by Cacti

My scan guage normally reads 13.9 volts regarding the 12 volt battery while I'm driving, yesterday while driving it read 13.3 volts, what is the normal operating range? Should I be concerned with the 13.3 volt reading? My Prius is a 2007, purchased new July 2007.

Poleikleng

Use your MFD in maintenance mode to confirm the reading. See my description for using your MFD in:

Checking 12v Battery Health - Hybrid Car Forums

It should not drop below 13.8 when the charging system is operating correctly.

JeffD

[Cacti]

Thanks Jeff,

This morning I moved the Prius in the driveway and the scan gauge read 13.9 volts. I will print your instructions regarding checking the battery health with the MFD maintenance mode.

Poleikleng

Originally Posted by jdenenberg

Use your MFD in maintenance mode to confirm the reading. See my description for using your MFD in:

Checking 12v Battery Health - Hybrid Car Forums

It should not drop below 13.8 when the charging system is operating correctly.

JeffD

[icarus]

A "12 volt" battery will in fact show ~12.6-12.7 vdc at rest,,, neither under load nor being charged. While under charge,, it is fine if it goes to ~14.2-14.6vdc. Under load,, with no charge happening,, it can read into the low 11 range. This is NORMAL. If you see voltages above 14.6 or below say 12.4 while the car is running,,,then have it checked.. other wise it is fine.

Icaru

[jdenenberg]

Originally Posted by icarus

A "12 volt" battery will in fact show ~12.6-12.7 vdc at rest,,, neither under load nor being charged. While under charge,, it is fine if it goes to ~14.2-14.6vdc. Under load,, with no charge happening,, it can read into the low 11 range. This is NORMAL. If you see voltages above 14.6 or below say 12.4 while the car is running,,,then have it checked.. other wise it is fine.

Icaru

Icarus,

The OP is not talking about any "12v battery" he is discussing a Prius AGM 12v battery. Our Prii use a "constant voltage" charging system. 14 volts are supplied by a DC-DC converter (from the 200v battery) to maintain the charge on the AGM battery anytime the car is in "Ready" or "Accesory" mode.

The accesory voltage will drop to about 12v when the charging system is off, but if it drops much below 12v there is a problem. Either you have depleted the charge, or the battery is due for replacement.

JeffD

[icarus]

Originally Posted by jdenenberg

Icarus,

The OP is not talking about any "12v battery" he is discussing a Prius AGM 12v battery. Our Prii use a "constant voltage" charging system. 14 volts are supplied by a DC-DC converter (from the 200v battery) to maintain the charge on the AGM battery anytime the car is in "Ready" or "Accesory" mode.

The accesory voltage will drop to about 12v when the charging system is off, but if it drops much below 12v there is a problem. Either you have depleted the charge, or the battery is due for replacement.

JeffD

You are correct about the AGM having it's charge voltage limited,, due largely to the battery not being able to accept water if it is overcharged like a conventional lead/acid battery. The reality is,, while the float/absorb/charge volts are a bit less with an AGM,, the at rest/under voltages are essentially the same as any other lead acid battery,,, as the basic battery chemistry is the same.

To the OP point,, at 13 vdc +- he is fine. If he is sub 12 under charge,,, he MAY have a problem.

Icarus

[richard schumacher]

The key point is to make certain that the charging system is not on while assessing the battery. Use the built-in self test, or use a voltmeter at the charging point under the hood with the car OFF. If it is less than 12.0V with no load the battery is near death.

[icarus]

The old joke,,,,

What's the voltage of a 12 volt battery???? 12.6 volts!

12 volts is almost dead!

Deep Cycle Battery FAQ

Icarus

[Patrick Wong]

On the occasions where I have measured voltage on the 12V bus while the Prius is READY, I've measured 13.8V +/- 0.1V. However I've seen some posters assert that the voltage may decline into the low 13V range depending upon ambient temps and 12V battery charge.

Meanwhile, the repair manual says that 13V to 15V is an acceptable range when the car is READY and all electrical accessories are on (from page 05-486-6, 2005 Prius Repair Manual). Therefore the OP should not be concerned with a measurement of 13.3V.

13 CHECK OPERATION OF W/ CONVERTER INVERTER ASSY
(a) Connect the C5 and C6 converter inverter connectors.
(b) Set the electrical tester with the AC/DC 400 A probe to the
wire harness of the C6 connector.
(c) Connect the I14 and I15 connectors (color: orange) to the
inverter.
(d) Install the inverter cover.
(e) Install the service plug grip.
(f) Turn the power switch ON (READY).
(g) Wait 5 minutes.
(h) Operate the electrical devices as listed below:

Set the lamp control switch to High beam.

Set the heater blower fun to HI.

Turn on the defogger.

Depress the brake pedal

Press all the switches of the window regulator master

switch at the same time.

Turn the steering wheel to right or left.

(i) Measure the amperage and voltage.

Standard:
Item Specified Condition
Output current 40 to 100 A

Battery voltage 13 to 15 V

[grand total]

Originally Posted by icarus

The old joke,,,,

What's the voltage of a 12 volt battery???? 12.6 volts!

12 volts is almost dead!

So, would you say 9.6V is dead? That's what mine is at before 'Ready'. However the dealer has tested it and says that the tester indicates that the battery needs to be charged, not replaced. I may have an argument on my hands here. Once 'Ready' I get 13.8V or 13.9V.