How to test hybrid battery?

I am reasonably certain that the traction battery in my 2005 Prius is failing (among other problems, some of which might well be caused by the failing battery). Not surprising after 300k miles.

My main question here is: is there a way to test the hybrid battery with DIY means? I'd hate to buy a replacement battery, and then find out that it was a different problem, after all.

I am trained as an electrical engineer, so I'm somewhat (but not completely) comfortable with working around the high voltage, as long as I know what to pay attention to to keep safe, and where to attach a voltmeter.

Also, some of the companies offering battery replacement seem to be fly-by-night, while others look like they might be reliable. I have seen some brand names for aftermarket parts (Doorman and A1 Cardone), too. Any tips for identifying a reliable company?

Symptoms are: battery spends a lot of time with a single red bar, and the only time I ever get it to green is after a trip 4000 feet down my mountain. The battery also doesn't power the car for as long as it used to. Recently, the car also started reporting problems with the ABS system (discussed in another thread here). Voltages on the 12V system are normal both when parked (12.4V) and in IG-ON (13.8V).

No battery-related dashboard lights.

 

Thanks! Yes, I looked at that option, and decided against it for various reasons. My question is specifically about how to test the battery, and then further decide.

 

Well, the car is clearly performing below specs, so some component has gone bad even though according to the codes, all components are "within specs". I have reason to believe that it's the traction battery, so that's what I'm looking to confirm.

 

My symptoms may well be different from most people's because of my driving pattern (I live at 4000 ft and commute almost daily to sea level and back).

But your remark of "doesn't sound like a failing battery" is exactly why I'd like to find a way to be reasonably sure before investing in possibly the wrong repair.

My benchmark for the battery going to the single red bar is my trip home. When I first moved here about two years ago, the battery would hold up just about to the top. Today, it gets to the single red bar around 1000 ft; the rest of the way, the ICE has to pull the car on its own. On more or less flat ground (within San Diego), the battery rarely ever reaches more than about three to four bars.

Now that you mention the "reaches green quickly", I think I may have that, but haven't paid much attention to it. The last five miles or so to my home are mostly downhill, and from the peak (where the battery is always at a single bar) to my home, that's enough to charge it to five or six bars. Going down the 4000 ft incline seems to charge it to roughly the same level, but then charging seems to slow down, and I reach green only later than I'm used to.

And, yes, the engine is having a few issues, too, but they started mostly after the battery charges. I attributed them mostly to the engine having to work harder than it used to.

 

Thank you, Patrick. Your expertise is a godsend!

The spark plugs were replaced about 20k miles ago, and didn't help with the problem. I just replaced the engine air filter. But the exhaust system is in bad shape, so that might be it. The catalytic converter had been plugged up for probably 50k miles at least, and I had got the P0420 (IIRC) code. We live in an area where the car doesn't need to get smogged every two years, so I considered this low priority.

The engine was also burning oil (around a quart every 1000 miles or so). In fact, I had considered having the engine rebuilt.

When my "battery" problem started, I did notice several engine-related things around the same time. I assumed that they were a result of the battery going bad and the engine working harder than normal, but of course it could also be the other way round.

1) the DTC code disappeared.
2) Smell of exhaust outside the car (and inside if I have the fan on)
3) Strangely enough, the engine is no longer burning oil.

The engine is now also knocking when I push it too hard. Switching to 91 octane and going slower helps.

On flat ground, the car drives like normal, except for the low battery.

 

Thank you! And it seems entirely possible that the engine issues might even be responsible for my ABS issue, too (I asked about that in another thread). Thanks!

 

That is good news. It did not even occur to me that the catalytic converter might have such consequences!

 

The only things I did, on recommendation from my oil changer guys, was switch to 10W30 and use their high-mileage additive.