12V battery issues?

Hi all--

A while back, I was trying to determine the source of some problems with achieving SHM (Super Highway Mode), and that it had no relation to the vehicle's SOC and would do the same regardless whether the Prius was in S3 or S4.

I think I may have found a culprit - the 12V battery. I came onto this because I realized that the only times I couldn't get SHM were at night (as, ironically enough, my pictures at the top of the "Issues with SHM" thread illustrate). As far as I know, it's original with the car. After letting the car sit overnight, the ScanGauge tells me that the battery reads 10.0 volts at rest, 9.6 when I turn the computer on, and 9.4 when I go to accessory mode. When I turn the power fully on, it jumps to 13.6-13.8 and stays there.

No warning lights, no strange behavior beyond the lack of SHM at nights. Is it time for the 12V to be shown the door? And if so, how difficult is the replacement? I despise the notion of paying a dealer $100+ for labor.

 

Hi stillageek--

I went ahead and ordered an Optima Yellowtop from Advance Autoparts, which set me back about $160. They said 3-4 days shipping. Here's to hoping my 9.9-volt battery doesn't turn my Prius into a dead start over the next week.

On a semi-related note, I wonder how much $ you can get from scrapping old batteries?

 

Hi uart--

Yep, I made sure the lights were off, radio was off, and windows rolled up before I turned the power. I could tell an audible difference in tone when the car was off re: electric windows - they were much, much slower, in fact, they almost seemed like they wouldn't make it.

I got the Optima Yellow Top shipped to my door today and after some 45 minutes of swearing I got the new battery in. It holds at 12.6 volts per the scangauge and also I'm seeing much better fuel economy. I'm at 7 pips and had ~270 miles at 58.x MPG before the battery, I've had 49 miles at 67.x since. Time will tell if it made all the difference because I made some pretty serious attempts at hypermiling