2007 Prius Red warning light and check engine lights on

you need to read the trouble codes. is it hot there? is the battery cooling fan and intake grille clean?

the modules have to be tested under load

 

Specifically you need to be able to read codes and data from the HV battery ecu. A good option is to get a mini VCI cable (with a bootleg copy of Techsyream - Toyota's diagnostic software) and install it on an old windows laptop. Another option is to get the DrPrius (or Hybrid Assistant app - android only) with a compatible OBD2 bluetooth adapter.
Then you will be able to see what codes are triggering the warning lights. Also can monitor battery block voltages while the car is driving- during discharge and charge loads. Much more useful than looking at static voltages while it's just sitting there.

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Just one notch less specifically, I would start by reading whatever codes are reported by any ECU in the car. Techstream has a "health check" button that makes this easy.

There may be codes in the battery ECU (probably are, given the fan behavior), but anyway the health check will find out. The ECU making the call to light the warning light is the HV ECU, so it will have one or more codes also (which might only be P3000, meaning to go look at the codes from the battery ECU). With the health check you won't miss any.

 

what are you reading the codes with?

 

So, the HV battery ecu monitors the voltage of 14 blocks. Each block is made up of 2 modules. (So 28 modules total- all connected in series). Each 7.2V module is a sealed assembly made up of six 1.2V Ni-mh cells. (So 28 x 7.2V = 201.6V - nominal, the actual voltage goes higher).

You have two blocks that each read about 1.5V lower than the rest. That is almost certainly indication of two bad modules.

You can search the forums here to review repairs options. New (Toyota or newpriusbatteries.com) -most $$$ and reliability- should last 10+years. Rebuilt/ "used" (greenbean, dormann, the guy across town)- slightly less $$, might get a couple years- be sure to know the warranty.

DIY -buy a complete pack from a wrecker (possibly best $$ to reliability to time ratio). Or get a few modules and just swap them ( and swap again, and again, aka "whack a mole"- least cost and reliability). Get some modules and hobby chargers to cycle all the modules individually(needs the most time and knowledge to achieve a good result). Last is to get some modules and a grid charger to cycle all the modules at one time (less time needed than hobby chargers but costs more for equipment)
Again, might get a couple years, depends on luck and how much you put into everything.

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