I've been forsaking Pearl lately, as it's hard to drive her on the ice covered roads, trying to avoid damaging her underside (yup, I'm lazy). So I've been using the FJ Cruiser, and driving Pearl once a week to "keep the battery up". Well, it didn't work! I noticed on the Scangauge that the 12V system voltage was running at 13.9 instead of the normal 13.8. That has always indicated that it wasn't fully charged, and it wasn't. On the weekend I had to help in a 1/2 marathon, and was posted in Pearl along the run to give assistance with my Amateur radio. So Pearl sat in "ready" for three to four hours. Now the 12V system voltage is back to 13.8. Just a "heads up" for those who think a half hour every week in "ready" will suffice. It won't.
13.8 and13.9 David are those #'s being taken with the engine running? I always check mine in the morning before starting the car and hope for 12.6!
Actually, on newer 2G, the DC/DC converter voltage will decline further to 13.2V if the headlights and cabin ventilation fan are not on, after ~20 minutes of run time has been logged, if the 12V battery is fully-charged. So I suspect that if you put your 12V battery on a charger you will be able to put even more charge into it. My "charger" is a lab power supply set to 13.8VDC. It can produce ~3A maximum current. I no longer use the automatic 2A/10A/50A Schumacher 12V charger that I have because it cuts off too soon, IMO. I find that if the Prius has not been driven for a week, I can charge the 12V battery for a full 24 hours before the charging current stops dropping. I would expect the charging current to decline down to ~0.05A if the battery is in good condition. If the battery is not in good condition, the current will stabilize at a higher current level, perhaps 0.1A - 0.2A.
Actually the voltage won't drop unless he does all of the above and puts the car in drive or reverse and the ambient temperature is above ~55 degrees...strange but true!
The above voltages are constant whether the engine is running or not, the lights are on or off, etc. Be aware, Pearl is a Canadian car, and so has the DRL system, along with "auto" headlamps. It was light out so the headlamps were in DRL dim condition with no taillamps, but I have never seen any other thing effect the 12V system voltage (as measured by the Scangauge). It will drop slightly when I turn on the hatch glass defrost, but will quickly recover to the above posted values. Even temperature doesn't seem to affect the voltage. It should, but it doesn't.
You're right, I don't know how the Canadian Prius behaves. DRLs are probably enough to keep the voltage high. But, since you were parked, observing the race, you were not in drive or reverse. Your charging voltage would remain high anyhow. I guess what I'm saying is that an American Prius would not reduce charging voltage after 22 minutes with the lights off and the car in park and no fan. The Aussie Prius behaves like this too. You got me with the DRLs.
A little more information. It appears being in "ready" about one hour per week is enough to keep the 12V battery charged.
