HV battery discharging rapidly at start of trip

Hi all, before I go on a quest for a new battery I wanted to stop by here to make sure that the battery is the problem in the first place. Extensive (software-based, haven't opened anything up - afraid to touch any shock-y parts) testing below.

In the last three weeks or so, when using the A/C at the beginning of a trip my HV battery charge drops from medium (4-5 bars) all the way down to low (1-2 bars), and after about 10 minutes of normal driving it's back to normal - stays in the middle of the battery gauge for the rest of the trip.

One way to mitigate this is to not use the A/C for the first 5 minutes of a trip, but the highs these days are 105F, so that's hardly a good option.

What concerns me the most about this situation, especially when the A/C is on, is that when the charge drops to one bar the car has sluggish acceleration and that's extra scary on a highway ramp.

Here are two reports generated by the Hybrid Assistant app connected (via bluetooth) to an OBDLink LX OBD-II adapter:

1. 25-mile trip showing rapid discharge at beginning: https://jenesuispasbavard.github.io/Report_2019-08-08_14-12-41.html
2. Stationary HV battery test (charge to 60%, run A/C, headlights, rear defroster until ICE restarts): https://jenesuispasbavard.github.io/Report_2019-08-12_10-42-57.html#hvhealth

The second report has a HV Health section that shows the battery discharge rate when parked and discharging with A/C etc. on. None of the blocks seem to be behaving too differently from the others - the deltaV looks ok, right? In the Blocks Stats table, does the larger-than-normal "% Time @ Min V" of Block 7 constitute a problem?

Manual HV health test results (start at 60%, run A/C, headlights, rear defroster until ICE restarts):

61% at 10:48:16
42% at 10:51:36
= 19% in 200 seconds = 10.52s/%​

Any ideas? Is this a case of the HV battery on its way out (RIP)? Or is it the 12V battery, inverter, or something else entirely? I've checked for error codes with Torque Pro and OBDLink, and they say all's clear.

 

The car's at 169,800 miles.

I just went out to check the inverter pump - seems to be functioning normally, the coolant is at the Full line and flowing through the reservoir.

It now runs without A/C like it used to last month with A/C. Battery does discharge at the start of a trip but only a couple of bars. In the Hybrid Assistant app, I've noticed that the car relies more on power from the battery at the beginning of a trip. I've attached a screenshot of this behavior from last year when it did this only when the battery was over-charged (green bars), but now it does it regardless of charge. It used to be that the red bar (ICE power) was almost always higher than the blue bar (electric power) when the battery was at a normal charge (~60%). But these days the blue bar is always higher (unless I floor it) in the first 5-ish minutes of a trip.



Haven't needed to fill up yet since this problem arose so I don't know if the MPG has changed. Fuel efficiency has been pretty stable over the 25,000 miles since I got it two years ago - around 42 mpg with 80% highway driving.

 

Nah, I've been using Hybrid Assistant since I got the car two years ago. Car behavior is definitely different now than it used to be. I've noticed now because the battery drops low enough that it starts having an impact on acceleration. This is the first time in 25,000 miles that I've experienced this.

The *only* other change (I've chalked it up to coincidence) is that I've moved from a place with covered parking to a spot under a tree, and this issue has cropped up around the same time. HV battery temperatures aren't vastly different than they used to be. And I parked in an open spot for the first year anyway.

Here's a comparison between how it used to be (May 30) and how it behaves now (Aug 8). At the trough of the SoC charge on the right, around 3 minutes in is when the acceleration of the car changes drastically - gets very sluggish, corresponds to when the battery level hits one bar on the dash.


In both cases, battery temperatures are similar (in fact, the battery was hotter in the older case when engine behaved normally).

 

A little over three hours from either one, unfortunately. I'm in Austin.

 

Very interesting. Thanks for the suggestion.

After reading this I've redone the battery test (charge to 80%, discharge to 40% by running A/C, headlights, rear defroster until ICE restarts), and results are similar to what I had when I bought the car two years ago in terms of battery % lost / minute. So the big battery seems to be in decent shape still.

The engine does seem to complain when I start the car. For a couple of minutes it has a few hiccups (not sure how to describe what's happening) - RPM meter on the Hybrid Assistant app says the usual 1100 rpm in S0-S4 / Idle Check modes - but the engine shakes occasionally, and sometimes seems to miss a beat (not sure how else to put it - I'm not an expert sorry).

A few fuelups back I did add 10 oz. of Chevron Techron concentrate each to two consecutive tanks; didn't notice much of a change.

Is it easy to DIY what you call the basics - check spark plugs, air filter, clean MAF?


If not, maybe some others have a suggestion as to where to take the car in to get the engine checked out in Austin, TX? I've been doing my routine maintenance at the dealer but haven't had to take it in with any issues yet; and I'm not sure if they'll have my best interests at heart. I bought this car for less than $6000 outright two years ago, and I'd rather not spend too much to fix it.

 

Cool thanks for the warning. I'll see how much of the basics you mentioned I can DIY.

Yeah, Texas is a big place, and Matt is almost four hours from me sadly. Also it seems they specialize in HV battery replacements, and aren't we not sure if that's the problem with my car?

 

MY MAN!

I didn't dare to do any of those things myself so I followed a friend's recommendation and took the car to a well-regarded local shop and sat down with someone there for 20 minutes going over some of the pictures I showed above. Explained that the battery life was still good going by discharge-time-with-A/C-on, and suggested they look at the engine. After some discussion, the following services were performed for just under $300:

1. Remove and replace air filter
2. Clean throttlebody
3. Clean mass airflow sensor
4. Engine oil change (unrelated scheduled maintenance)
5. (Spark plugs were in good condition, they said)

And after some testing-from-cold-start for a few days, I'm fairly confident that the engine is now supporting the battery as it's meant to. The battery level is no longer plummeting to one bar and affecting acceleration; with max A/C on with a cold start it now recovers in less than five minutes instead of the crash to one bar and recovery after 12-15 minutes. Here's a before (Aug '19) vs. after (Oct '19):

 

...

The plugs are less than 50,000 miles old, and they don't need to be replaced yet. Good on them for being honest about it.


For everyone else, just got back from an 800-mile road trip, with no issues!