Battery Module Numbering - Do We Really Have it Right?

It can be different in different generations but for a Gen 2, the module numbering goes from the right to the left as you look at the battery from the rear of the car looking to the front.

FYI, also note where you said cells you mean modules and where you said modules you mean blocks.

 

Is this not in any of the manuals like the three volume set for the generation 2 or the three or any of this kind of silliness You got to be kidding me right I mean literally like in the factory bound paper manuals there's three of them for the generation too I think It's a set I would find it hard to believe that Toyota would just leave this out then again when the manual is written the battery probably initially wasn't made to be serviced just replaced like a Duracell you know like we did in the old days then humans out in the field got involved and wanted to play and hence we're back to prison antics like putting d cells in a refrigerator so they'll work a few more seconds the next day I mean okay. And then except for the sake of conversation doesn't really seem like it would make a big deal or a bunch of hoopla You take the battery out you undo the bus bars and nuts you measure modules blocks whatever you want to call all this stuff You find out what's out of spec you replace squeeze up install charge and discharge and play all the games and go on about your business till you have to do it again or you just replace that 9-year-old battery and be done with it so you either like to play or it's cheaper for you to play or not.

 

Rick,

I will throw my name out there as being marginally qualified to help you with this.

There are 15 voltage sensor tabs on a Gen 2. One under each orange cable, one on each busbar.
It requires a little bit of electrical understanding about equivalent points for voltage readings.

The heavy orange cable going to the (-) post of a module is the #1 module. This also has the first sensor and is the ZERO voltage reference for all the others. Module 1 and module 2 make Block #1, modules 3 and 4 make block #2, and so on.

Everywhere there is a sensor wire, there is also a bus bar (except modules 1 and 28). Look at it like this:
Module 1 has the heavy orange cable on the (-) terminal and a sensor tab, it is the zero V reference.
Module 1 (+) is connected to Module 2 (-) on the other side of the battery. Module 2 (+) and Module 3 (-) are connected by a busbar and have a sensor tab fastened to them. This sensor reads the combined voltage of module 1 + module 2 compared to the previous sensor tab (in this case the zero point).

This continues for each set of two modules (blocks) until module 28, where it's a heavy orange cable on the (+) terminal with a sensor tab.

Does it matter if the sensor is touching the busbar at the module 2 stud or the module 3 stud? NO, they are the same exact point, electrically.

If I have a bare wire that's 50 feet long with 120vac on it, I'll get shocked exactly the same whether I touch it at the 1 ft mark or the 49ft mark. It doesn't matter because that voltage is on the entire length of the wire (or in our case, the entire length of the busbar)

For electrical voltage measurement (keeping it simple theory) every piece of metal touching that busbar is at the same exact voltage. (If they aren't then there is a bad connection)

Now....for proof of the numbering system

Service Manuals - Google Drive

Look at the section titled HB and then go to page HB-8.
The right side of the page shows how the electrical sensors wiring is connected to the battery modules. A battery is represented in an electrical drawing as two lines, one short and one long. The short line is the (-) and the long line is (+).

 

The one counterexample to this that I know of was the Gen 1 Prius (2001–2003), where the #1 module was the one at the + end. Whether all the generations after that follow a "count from − end" rule, I'm not sure; usually knowing just one counterexample is enough to make me suspicious of a rule, so I feel more comfortable just looking each one up in the right manual.

One idea you can use to convince yourself is to look in the wiring diagram to see if the voltage sense wires are shown with numbers and color codes. A 2006 Gen 2 diagram shows them like this:



So in that diagram you can see that the count starts with GBB0 (the reference) and it's the blue wire with the black stripe, and the last one is VBB14 and gray with black. (And because of the way the service plug isn't right in the middle, you can pretty much tell at a glance where those are.)

While this is a Gen 2 thread, may as well state for the record:

Gen 3 has a very similar diagram, but with different colors, red for GB0 and black for VB14. (Which of course will explode the head of everybody who expects red to be + and black to be −.)

The Gen 1 diagram was a headache because it showed the colors and pin assignments but no mnemonics numbering the modules (and Gen 1 put the service plug spang in the middle of the stack of modules, so you didn't have long end/short end to go by). One had to go to the repair manual, where the page for the P3030 code had a picture that repeated the same pin assignments and colors and added mnemonics, where the + first one (gray with black) was VBB1, and the − last one (blue with black) was GBB19. Got confirmed in this post by inspecting a new Gen 1 sense harness.

And at least through the first three generations of wiring diagram, it seems nobody ever corrected the spelling 'busber'.

 

The module numbering approach you described, starting from the negative cable and pairing cells sequentially (cells 1 & 2 as module #1, cells 3 & 4 as module #2, etc.), is a common but not universally standardized method. The key rationale behind this method is simplicity and logical order in connecting and managing cells, ensuring clear tracking from the starting point (negative terminal) to the positive. However, there's no strict industry-wide standard, and variations may exist based on manufacturer or application-specific guidelines. To ensure accuracy, always refer to the specific battery system’s documentation or manufacturer's guidance for the correct module numbering convention.

 

You mean, "The module numbering approach you described, starting from the negative cable and pairing modules sequentially (modules 1 & 2 as block #1, modules 3 & 4 as block #2, etc.), is a common but not universally standardized method."

 

Yeah and then you get the full electric car batteries they're a whole bunch of fun I see the guys up at electromotive garage and all that they having tons of fun with all this battery stuff oh well . Cells are inside of modules various block configs are made up of arranged modules and on and on . When it starts becoming fubar. Rather than do a whole bunch of fixing and eliminating cells etc probably time to just get a new one like the manufacturer suggest. It's only problematic because of the cost.

 

Like @dolj noted and I'll add, for the Priuses NiMH HV batteries, that each module consists of six cells in series that are not accessible as individual cells. I almost thought you were a chatgpt or some other ai bot replying.