Hybrid Battery Recharge?

Thanks for the information. I do own 4 vehicles and I'm the only driver so I can picture a possible scenario where this could happen. Especially if I were to be gone on any extended trips. The reference to "modules" is what threw me since I have always thought of cells when it comes to batteries. All good info. that makes me think maybe I should read the owners manual in more detail. Just curious, how would the "modules"/cells get reverse charged with the car not starting or connected to a charger?

 

Don't get confused between the 12v battery (cost $200) and the HV (high voltage/traction) battery. It's the 12v battery that gets discharged by the door being left open.

 

To clear things up a bit more, one NiMH cell is always worth a nominal 1.2 volts (a fact of nature fixed by the NiMH chemistry). In the Prius battery these are packaged in modules of six cells each, in series, so each module is nominally 7.2 volts and roughly the size/shape of a thin brick. The hybrid battery assembly stacks 38 of these modules in series, or 228 NiMH cells, for a nominal 273.6 volts. It's totally series-wired, so whatever current is flowing in or out of the battery at any moment, exactly that current is flowing in each of the 228 cells.

The self-discharge of NiMH cells is an internal phenomenon. There doesn't have to be any current drawn from the battery, they'll all discharge gradually just sitting there. And they won't discharge at exactly matching rates.

At the end of several months, you have a series stack of 228 cells in assorted different states of charge, all of them low, but some just low and some really low. The next event is what happens when you try to turn the car on.

If you're lucky, the battery ECU will nix the whole idea based on the charge condition, and the car won't even try to go ready. Otherwise, the attempt will be allowed and the System Main Relay will pull in, connecting the battery to the car.

At that point, because a lot of the cells still have positive voltages, and the capacitors under the hood can accept plenty of inrush current, current will flow. It will flow through all of the cells (because they're all in series), with the stronger cells providing the oomph, and the cells that are more fully discharged having the current forced through them by the stronger ones. The current is flowing in the direction of discharge, and as long as there are stronger cells around, it will keep flowing even as some of the weaker cells reach zero volts and further into negative territory. That's the "reverse charge"; not so much something that happens during the long gradual discharge, but a consequence of the subsequent attempt to use the battery.

Any reversed cells aren't coming back, meaning the modules that contain them are ready for the recycler.

-Chap

 

If you decide to order the dealer battery, ask them if they are 100% certain it will solve your problem and make your car happy.

I've had dealers tell customers they need a battery, customer agrees to buy a battery then they say "oh yeah, we didn't notice before but you also need a transaxle for another $5k".

 

I wanted to throughly agree with Paul and share one mitigation:

Dealers have technicians with variable skills and experience levels. Not unique to Toyota, some organizations have 'procedures' designed to handle '90%' and frown on independent thinking and diagnosis. Paul is right that you want a reasonable guarantee that if this $3k expense doesn't work, they will 'do the right thing.' Then you have our little corner of the Internet.

The folks who regularly post here are enthusiasts, engineers, and technologists who really like and are fascinated with the technology. Over the years we've sought out the 'interesting' aspects of our cars from operation through debug and repair. Happily, folks here are pretty well balanced and mature enough to share their individual skills and attitudes. But as Paul points out, we also realize that skills at Toyota service centers are a 'mixed bag.'

Universally we're fond of advising owners to have their own, Prius-aware, OBD scanners, $40-500, that can read out traction battery metrics as well as the unique Prius electronic control modules. There are half a dozen control computers but three in particular provide the critical diagnostic codes and metrics. Even if the owner is non-technical, bringing the results from a Prius-aware scanner gives us a chance to understand what is going on.

Good luck with the repair,
Bob Wilson

 

After much research on the web - Luscious Garage , Art's, this and other Prius groups - I went with a Toyota replacement battery for my 2002. As I recall, it was installed at my Toyota dealer here in Albuquerque for just about $2600 including tax. Came with the 1 year Toyota warranty. There is a sale I see on ScanGaugeII and take Bob's excellent advice. and pick one up. You can program it yourself with patience.
Ed K