So I thought the battery issue was over but it is not. After buying the wrong battery on Ebay (too big) I went and paid for the right battery at NAPA. I charged it up to 14.7 volts @ 2amps and put it into the car. All the voltages listed below are being monitored by a dedicated voltmeter. I checked it to a bench supply and it is accurate. Next morning the battery was at 11.9 volts the same as the old battery. I drove it to work and back. The second morning the battery was at 12.9 volts. Good. However when driving home the battery voltage was 15.9 volts which is way, way too high. It dropped to 15.1 fairly soon but according to daat on teh internet an AGM battery should only be charged to 2.4v per cell or 14.4 volts. I have mounted a data logger onto the battery that will monitor the discharge current and voltage every 30 seconds for the next five days. But the data so far makes no sense. It appears that the battery is being overcharged and drained (sometimes) overnight. I'm a little panicky because I don't want to destroy a brand new battery that cost 250$.
disconnect it. you need to measure the quiescent drain when the car is off, and look at the service manual for normal.
I think there may be a couple of issues with the way you are measuring voltages on your battery. To get an accurate measurement, you will need to let the battery's surface charge dissipate after it has been charged, even if that charge is coming from the car's DC to DC converter, and you will need to ensure that none of the car's systems are drawing down the voltage when you are taking that measurement. That would usually mean you should leave the hood unlatched overnight, and then approach the car in the morning without the key in your pocket and measure the voltage at the front jump points. You should get a reading of 12.5V or better under those conditions. Unless you are getting trouble codes indicating your DC to DC converter is malfunctioning, I would not be concerned about the fact that you are seeing 15.9V while driving, when the converter should only be supplying 14.4V or thereabouts. I would guess the 15.9 is the surface charge, which is not the true voltage of the battery.
14.7V? That would be what the charger was putting out, not the voltage of the battery once it was off the charger. It should have been something like 12.7V at 100%, open circuit.
Where on the car are you measuring voltage while the car is running? When I connect my leads to the battery clamps, I have never seen a Gen2 that was outside the 14.0-14.4V range while "ready". If you do measure over 15V at the battery, I would use a scantool to look at data in a few ecu's (hybrid control, ECM) to see if that matches what in in the data. Maybe there is a voltage drop between an ecu and the 12V system- resulting in the target V for the DC-DC converter (falsely) being set too high. There are a number of posts concerning key off draw. You want to manually close the tailgate latch while the hatch is open so that you can access battery connections while the car is at normal "fully off" conditions (doors also closed and SKS key far away from car). Securely attach an ammeter (usually most digital volt-ohm meters have this function - make sure the internal fuse is good!) between the battery negative clamp and a clean metal (ground) on the body. Remove the battery negative connection bolt at the body (while the ammeter stays connected). About 15 minutes after the car is turned off and the T/G latch is closed, the draw should be below 25mA (0.025 amps). Don't forget to release the tailgate latch BEFORE trying to close the hatch! Posted via the PriusChat mobile app.
I grabbed the data for a 24 hour stretch (midnight to midnight) from my 12V. It'll be a little different from a Gen 2 due to being a wet lead acid rather than AGM as well as the small charge it gets when I plug in my Prime to charge the traction battery. But you can still see the spikes when it's being driven as well as the surface charge that bleeds off after driving or charging. This chart shows two wall charges of the traction battery and two drives of roughly 45 minutes each.
Thanks everyone for the replies. I have had a dedicated voltage/current data logger hooked up to the battery for two days now and will take a while analyzing the data. (I'm OK with electronics bad with computers). In the mean time, the 11.9 volts seems to be a one time event. During the last two mornings the dedicated voltmeter showed good morning battery voltages of 12.6 to 12.9 volts. Which is good. If that number continues to hold the only remaining worry is the >15 volts charging while driving. The few times I have glanced at the voltmeter this weekend(I prefer to drive rather than collect data) I have not seen the >15 volts readings. Really, thanks again all. I will spend more time looking at your posts and figuring out what to say.
