12V Battery Check

Based on what I saw from the vehicle's charging system with a depleted 12V battery when my car was in the body shop for 2 weeks (waiting for a bumper replacement necessitated by someone rear-ending me), you need to drive it for the equivalent of about 45 minutes per week to keep the 12V battery "full"; a 5-10 minute drive a couple of times a week simply won't cut it- you'll get some charge, but not enough to fully charge the 12V battery, and on lead-acid batteries, chronic undercharging can lead to sulfation and premature battery death..

 

<div class='quotetop'>QUOTE(c4 @ May 13 2006, 01:10 AM) [snapback]254634[/snapback]</div>

Are you saying it took 45 minutes to recharge a fully-discharged 12V battery?

 

Not fully discharged, and not charged to 100% capacity- I'd say that the battery was down to about 20-30%, and it was recharged up to about 85%.. The exact scenario was that the car had sat for two weeks in the body shop, and when I got it back, the 12V was low.. I have a miniscanner in my Classic Prius, so I monitor the voltages and currents in the system.. Normally, with a fully charged 12V battery, when the car is on, but engine is in idle-stop, they drain to the hybrid battery reads in the vicinity of 1.5 A, and the aux battery voltage sits at 13.8V.. When I got the car back, the idle-stop current draw from the hybrid battery was up to 3-3.5 A (ie, an additional 500-600W was being drawn from the hybrid battery through the converter to charge the depleted 12V battery) and the converter output was boosted to 14.0V (this is the first time I've ever seen this occur on my car).. This condition persisted for two days, and I normally drive about 60 km/day, 2x25 minute commutes per day. I also have a larger battery than OEM (I put in an AGM battery sized for a Honda Civic, which is roughly 55 Ah, or close to double the capacity of the OEM battery).. So extrapolating and rounding to an convenient period of time: I have a battery roughly 2x the capacity of the OEM, and it lasted for 2 weeks sitting, I needed roughly 100 minutes of driving (not including the output from my 15W solar panel); therefore on the OEM battery for 1 week, I'd estimate you'd need half the charging time, or somewhere in the ballpark of 45 minutes...

The charge rate is faster than with a low-rate home battery charger, but not as fast as it could be.. Lead acid batteries can take very high charge rates if you don't care about hydrogen production..

 

<div class='quotetop'>QUOTE(MinneMiss @ May 12 2006, 09:44 PM) [snapback]254477[/snapback]</div>

You can buy a cheap voltmeter and check the voltage at the terminal under the hood routinely. Is the car garage-kept? You could always buy a $20 float charger at Harbor Freight to keep the 12 volt battery topped off all the time. I have to do that to my "old" daily-driver, now the the Prius is my new DD.
If the Prius is kept outdoors, you could do the "always ON cigarette lighter" mod, and plug one of those cheap solar panel chargers into the outlet. I would have done that, except the car is in the garage.

 

<div class='quotetop'>QUOTE(MinneMiss @ May 13 2006, 09:44 AM) [snapback]254477[/snapback]</div>

Have you heard of the Diagnostic Screens?

You can read the Aux. battery voltage from there. Not sure about the accuracy though, but it should give you some idea if the voltages dropped too much.

 

I was told, well a while ago, that the only way to test a lead acid battery is with a hydrometer. Is that not the best test? I was told that Voltage was inaccurate!

 

<div class='quotetop'>QUOTE(hdrygas @ May 15 2006, 10:58 AM) [snapback]255488[/snapback]</div>

The Aux battery in the Prius is a completely sealed valve-regulated absorbed glass mat (AGM) battery. How do you use a hydrometer in a sealed battery?

 

<div class='quotetop'>QUOTE(MinneMiss @ May 15 2006, 08:48 PM) [snapback]255593[/snapback]</div>

Yes, I would recommend you to read up first to understand what each menu item does before playing around with it. Do a search for diagnostic screen and you should get a lot more info.

There are at least 2 methods to get into diagnostic mode:

Method 1
Start the Prius. While pressing and holding â€INFO†switch, operate light control switch, OFF, TAIL, OFF, TAIL, OFF, TAIL, OFF. The diagnostic mode starts and the service check screen (â€System Check Modeâ€) will be displayed. Service inspection starts automatically and the result will be displayed after a short pause. You’ll be able to see how many satellites are currently being received as well as Greenwich Mean Time, among other things. Press “Menu†to see the menu. To exit either turn the power switch off, or press the â€DISPLAY†switch for 3 seconds.

Method 2
Follow this link:Accessing the Menus:
A lot of photos with explanations.