BATTERY AT 2 PIP'S!!!!

I honestly wouldn't worry about it. Do you try to only use electric power when you're close to home? If so, the battery may actually be that low once you park that car. However, it did not update the status of the battery until the car was restarted. The only reason I think this may be the culprit is because if I'm on electric only for a while, the battery holds its charge for a while, but then just drops quickly down to 2-3 bars within a minute or so. I wouldn't worry about it man.

 

Don't worry! I would think it is just fine! When you re-start, The computer readjusts it's figures.

 

A hot battery would show a higher voltage than a cold one, at the same state of charge. I have lost 1 - 2 bars from parking it to the next morning, on occasions.

 

A hot NiMH battery has a -lower- voltage than a cool one. Same as NiCd. That's why early Bell 206 helicopters could have their NiCd battery go into thermal runaway. They used a simple charger. It would heat up and draw more current, heating it up more. Not good! I was on board one when we had to land -quickly- to shut down to prevent a fire! It's interesting when you don't have time to select a nice landing area.

It's not unusual for the battery meter to do that. It doesn't happen very often but it happens. It's meaningless.

 

I do not know anything about the Bell Copters. Is this unique for charging?
Take a look at the PDF linked below, Figure 1 At least when discharging, the NiMH retains a higher voltage in a higher temperature.
http://pdfserv.maximintegrated.com/en/an/AN121.pdf

Million dollar question is what kind of temperature compensation algorithm Toyota has written into the Prius and how accurate their model is.

 

Toyota uses coulomb counting. Voltage is secondary. Do note that the temperature coefficient is dependent on the type of cell as well. The current Prius uses Prismatic cells, not cylindrical sintered plate ones.

At any rate, note the referred app. note says it's very difficult to calculate or measure the charge level in the cells. And it is! So regard the "battery meter" with suspicion. It's an engineering guess.

 

Also anything on the display from 1 bar to full 8 bars, is perfectly OK. 1bar is still above 40%. 8 bars is still below 80%. You can't hurt this car unless you really really try hard and go out of your way to do it. That includes running out of gas and then running down the battery pack or attaching an external charger and charging it up high

 

Just double checked my Sanyo battery manual. NiMH cylindrical cells are negative temperature characteristic as well. That is, even during discharge, hotter means lower voltage throughout the discharge curve. Same for charging. My earlier comment was for prismatic NiCd cells. I suspect they all (both cylindrical and prismatic and NiMH and NiCd) exhibit the same characteristic. So I'm not sure what that app. note was about. We're not talking about a lot of voltage here, perhaps 0.1V at any point except the start and finish with an 80 deg C temp difference (the curves in the manual went from -20C to +60C). However, this is why Toyota uses coulomb counting. Fully charged (80%) to fully discharged (30%) the cell voltage changes about 0.2V max. Temperature effects are large!

My understanding is the Toyota charger/charge control system uses voltage -once in a while- to bring the measurements back in line. They can do this by watching for the cells to reach 80% charge. At that point continued charging causes rapid cell temperature rise. I don't know if they utilize that trait, but it's there if they want to. They do monitor battery temperature.

I know some on this forum have some of this information. Perhaps they will comment.

Bottom line is, measuring battery charge level is iffy at best. Now you can see why! The meter is there as an approximation and for bling. Treat it as such.