Is my traction battery going bad?

Yes, but even with my significantly degraded HV battery (refer to the second figure in my previous post to see roughly how mine now behaves), I am getting hardly any loss of MPG. I'm currently at about 4.3L/100lm (55 MPG), pretty much the same as it always has been. So based on my own personal experience, I'm not totally convinced that a new battery will cure the MPG issue.

Where I do lose a bit of MPG is where it charges to the "top referenced state" explained earlier, and then it subsequently undershoots, dropping bars 5 and 4 (and sometimes even 3) very rapidly. The Prius just behaves like a total slug when the SOC is down around 2 bars, and it really doesn't operate very efficiently for the next 5 minutes or so until it regains that charge.

When I'm out driving on mostly flat roads however, the SOC just sits on six blue bars most of the time and you simply won't even know that the battery wasn't perfect. It operates totally normally and there is no degradation of MPG at all.

Again, if you look at the graph from my previous post you will see why the SOC seems a bit erratic at times. Essentially it sometimes just doesn't have as much charge as it thinks it does (in what I've called the "top referenced" state), and this makes it plunge unexpectedly quickly at times. Particularly at start up when the engine is cold (which btw is when the demand on the traction battery is often very high).

BTW. Talking about the engine being cold, I strongly recommend that you let the engine warm for 40 to 60 seconds before you drive off from a cold start (leave pruis in "P" and tap the accelerator to make the engine come on). This GREATLY reduces the stress on the HV battery. This is particularly important if you need to either climb a hill or accelerate quickly from a cold or cool engine. Please do give this a try!

 

maybe it's time to think diy?

 

you have to test the cells under load, but i think you can determine the potentially bad ones.

 

me too, but i have no idea.

 

Bisco is correct that you should to test under load. You can do this easily with the HV Battery still in place in your car once you have your MVCI up and running by running the test in the following link:

Predictive Battery Failure Analysis For The Prius Hybrid | Art's Automotive

hope this helps.

 

NO When you are driving pay attention to driving! The charge and discharge (or load) test is done safely sitting still.

 

you'd think the software would log it. i suppose someone else can drive.

 

See also strawbrad's post on the first page of this thread for a succinct test:

This thread | post #12

 

Art's Automotive test does log and graph the min and max block voltages. A block is a pair of modules. That would be a safe test to do while driving as you can look at the data after you stop. The Toyota manual puts a little different spin on the tests. They are all variations of the same theme. Load the batteries, charge the batteries, look at the voltages in real time. I like to highlight (just click on the data line) of the three or four blocks that seem to stand out on charge or discharge. That makes them easy to watch on the other side, charge or discharge. The Toyota manual recommends replacing the pack if there is more than .3 volt difference between the max and min. That is not enough to light the triangle or trip a code. There are lots of Prius running with over .3 volt variation.

Many Independent shops are now installing NEW Toyota batteries for far less than the dealers will. Waste bothers me. A failed pack will often have 20 or more usable modules. A Toyota dealer will send those good modules straight to the recycling yard. An independent shop will use those modules for rebuilds. The returned core will have truly junk modules fit to be melted down.

Brad

 

As far as engine coming on from a light, you have to know about of the stages of hybrid system warm up. Also Gen2 is not designed to go very fast on EV mode. Only if you are in the final warm-up stage and went extremely slowly should ICE not come on.

As UART says, as hard as it is to understand, low MPG is usually not the big issue with weak batt.

 

Uart was describing a gracefully ageing battery that has a (relatively) homogenous drop in capacity across the modules.

 

Yes, that's exactly what I was thinking SageBrush. My battery has definitely lost some amp-hour capacity, however I seem to be fortunate in that it appears to have retained its "grunt".

If jdonalds' problem is more related to higher internal resistance rather than a simple loss of amp hours, then that might explain the different behavior he is seeing. One thing that seems a bit odd about that however, is that I thought the Prius would throw a code pretty quickly if that happened. I know that the Prius will allow for quite a large loss of capacity without throwing a code, but I thought it was a lot less tolerant of other faults.

Coincidentally, I'm just shy of 245000 km right now, which is almost exactly 152k miles as well.