12V Battery Voltage Management

Thank you for your note.
Do you connect under the hood, or directly to the battery, removing negative/round from battey to the car?

 

you can connect under the hood. Do not remove negative, you will lose all presets,

 

The charger comes with an accessory cable that allows a permanent connection directly to the battery terminals and terminates in a single connector that matches a connector on a long cable from the charger. To use the charger it is only necessary to insert one connector into the other and turn on the mains supply to the charger. This charger does not require disconnection of the battery for maintenance charging, but if the battery is deeply discharged it is essential to disconnect the battery from the vehicle before making a recovery attempt.

The connector attached to the battery has a tethered cover which I put in place when the connector is not in use . I routed the cable from the battery to the opening giving access to the rear lights on the same side as the battery so I only have to remove the cover to this rear light opening to get at the connector. When I replace the rear light opening cover, the charging connector is hidden.

 

Yesterday I measured with a multimeter under the hood 90 min after stopping car:

- 12.7V before opening driver's door
- 12.4V during "pumping",
- 12.5V inner lighting only

Then I went to dinner (+ 1 hour), and came back, read on-board service menu value (which is the same as the OBD retrived value): 11.7V!

So it must be the car ECU that gives low values...I'm quite surprised, but at the same time felt relieved.

I have a portable charger rated 4Amp but I've never seen it over 3A except once for a SUV battery (90Ah) charging.
Regularly I feed a 45Ah battery of another car that makes short trips, and see 2A on the meter.

Is this charger elegible for charging Prius under the hood without disconnecting batt from car?

 

I have a 2012 and took pictures of the battery recently posted.

http://priuschat.com/attachments/img_1980_md-jpg.45340/?temp_hash=3f38cd2b44f8902438a41a0952f59b30

The note on the battery says not exceed 4.2A for more than 10 hours ... so above charger seems OK but check YOUR manual as well. Of course prius must be OFF which charging.

And I do not think you need to disconnect. I have charged my previous prius with a 2A charger when that battery was discharged.

Well I am not sure if I understand this correctly ... if the voltage dropped to 11.7V after another hour that is a big drop... I don not have the screen so not sure what that measure and when it captures that ....

 

The on-board info screen gives that value (navi models allow to get to a very simple signal menu, which is the same value that OBD reader gives), but a bit different from measured...



Right now I have: 11.8V on the screen, and 12.42V measured with a multimeter. There is the "drop"...

 

So the prius is in axuliary mode correct ??? Obviusly you had to open the door and push the ON button to get this far... if that is the case this is NO LONGER the 'sitting' voltage the manual refers to. Not sure what else else is powered but this voltage is under load no question. ... If it was 12.42 measure before turn on then your 12V battery is in good shape.

The ODBC port is actually connected to the battery ALL THE time so a scanner connected to the port would could measure the real 'sitting' voltage without any other load. I can enter my car from the passenger door and push the on button on the dasboard monted SG and it will show the battery voltage under no load (the security systme plus SG maybe a few dozen mW

 

What szgabor said; once you're in aux mode, you're draining the battery, and it's going to be lower (the 12.42 V you measured, instead of 12.7 V at rest). Also, there's probably a drop on the way to the Nav system, or wherever the voltage is measured - as the electricity travels along the wire, the voltage will drop. The more current is being used, the higher the drop (Ohm's Law). And it's quite likely that there are various filtering components or even a switching power supply that further reduces the voltage. To get the true battery voltage, it needs to be measured with no load for two reasons - one is the drop along the wires, and the other is the battery's internal resistance (which is a way of explaining why it drops even when you measure right at the battery terminals when it's under load).

My car reports about the same - maybe like 11.5 V on the Nav when the true battery voltage is more like 12.3 V or so.

 

Exactly what I meant .. in aux mode I would expect voltage under even 12.0V measured at the ODBC (as explained that includes the battery internals) ... fully charged healthy battery 11.7-11.9 less healthy 11.5-11.7 anything less 11.5V should be checked (temperature and SOC affects this as well).

What the manual states for battery health voltages are the measurements ON THE BATTERY without load !!! It is very easy to do if you have your own garage ... park the car pop the hood and come back in a few hours (2-3 hours after stopping or even overnight !! ). At that point you do not need to open any doors pushing any button just measure with the multimeter ... THAT will give the most reliable/comparable voltage measurement... (I KNOW this is not always feasible )

just my 2c