Alright, I got my scope working with my laptop yay. So it seems it's not exactly uncommon for the battery to be under 12.6v the prius draws a lot for a while before it does to low draw 120ma in my case. It sits drawing 2 amps for quite a while, seems to be related to the brake vacuum monitoring system, if you touch the brake pedal it jumps back up to the 2 amp draw (25w). Interior lights seem to draw around 2 amp as well which makes sense if they are 10w per bulb. It takes a few minutes at 1amp draw before it drops lower. I didn't wait any longer to see if it drops any more.
Seems like one of the ways to make the 12v battery hold a charge for longer would be to change out the interior lights to all LED. Hitting the brake and kicking off the vacuum pump seems to draw around 28 amps on my car, there's a sudden spike of around 6 amp that's really short lived to kick on the electric motor of what I'd guess is the brake booster.
Once I hit the start button, it jumps from battery voltage (started out 12.6v after a short drive, was 12.52 when I checked it with the hatch open (2 amp draw on it). The charging system doesn't mess around, it hit over 60 amps of charging, beyond my low amp probe's ability, I have a high amp probe, I just didn't swap it out to get the peak. It tapered down quickly and then sat around 8 amp of charging. Battery charging drops to around 1 amp and the power fluctuations go past the 0a line a bit (draw from battery vs charging battery). From the drive, the battery was on 1 amp charge most of the time, that seems to be roughly the float charge on this battery in it's current state.
I didn't compare the scan gauge voltage vs real battery voltage, past experience the scan gauge generally sees a lower voltage vs directly at the battery.
Oh also when you insert the "key" in the ignition, it wakes up some system and it draw around 2 amps.
It seems like a bare min spec for the battery should be around 60 amp peak output and enough capacity to handle around a 2 amp draw for 10 mins after turning off the car + 0.2 amp load for say 1 week. My quick math comes out to 34ah of capacity, seems like the battery I got the car with matches those specs pretty well, that was unexpected lol.
Based on those figures, there's roughly 430wh wasted per week just by the draws on the battery with the car "off" using higher values to include a bit of safety margin. It would be interesting to find the largest power draws as it's pretty common for a car to sit not being driven for a week at my place. My Matrix does a great job managing a low power draw and keeping the battery good, it can sit over a month between starts and it fires up no problem. My Lexus LS400 on the other hand has a dead battery after about a week. My F250 powerstroke diesel has never given me problems except once when I left the lights on and it can sit for a month+ with no starts too.
If the largest draw item(s) aren't too critical to keep powered, I might modify things so those draws are disconnected and only reconnected when in ready mode or similar. Like I mentioned before, I don't care much about the security system, at least for when it's sitting at my house. The wireless key fob isn't needed when it's at my house, things like that. I think I'll be swapping out the interior lights to LED to help lower the draws on the battery. It seems like the battery is performing fine, just the capacity might be lower than it once was.
I uploaded the scope reading, but this server resizes the image so small it's not super readable. Red line is voltage, blue is amps.
Reuploaded to a different server, looks way better.
