Dr. Prius Says #5 31 milli-ohms; Does That Cell Need Replacing?

I'm not sure there is a definitive Internal Resistance for a particular block that will cause your car to throw a code. FWIW, 31 milli ohms does seem rather high, but what you need to focus on is the delta between the block with the lowest voltage vs. the one with the highest voltage. If that exceeds a certain level (somewhere around .3V, I believe) for a significant amount of time, you will get a code for a weak block. You would expect to see the weak block more than .3V below the typical voltage for the other blocks when the battery is discharging, or possibly more than .3V above the typical voltage of the other blocks when the battery is charging. A high IR does indicate that one of the 2 modules that make up a block is not able to store as much energy as the modules in the stronger blocks when the battery is in charge mode, although that may not be obvious when measuring its voltage. Rather than capturing the energy that is being forced into it, the weak module will dissipate some of that energy in the form of heat, and may have a higher surface charge than the stronger modules. A surface charge will quickly disappear when the module is put under load. That explains why the weak module will appear to have a higher voltage than normal when the battery is charging, but a lower voltage than normal when it is discharging. So generally the block with the high IR will contain the weak module, but that is not the standard the battery ECU uses when it decides to throw up a code.

 

31 milli ohms is less than 1 ohm, almost a dead short of 0 ohms.

The app may have stated 31 Mega ohms which would be a more reasonable high value.

 

I don't really follow the reasoning here but, FWIW, Techstream displays Ω, not MΩ, the starting point being 0.019 Ω (19mΩ).

 

sorry nub here to traction pack issues and dr prius. but not grid charging.

Are there any other noteworthy results from the dr prius battery test you might want to post?

 

The screen shot you attached shows does not show a large difference between the block with the highest voltage and the one with the lowest voltage, but I really think we need a larger sample size to draw any firm conclusions. Either Torque Pro or Hybrid Assistant will allow you to log or graph the voltages of the various blocks as you drive down the road, which would tell a more complete story, as the battery charges and then discharges. If the delta never gets above .3V for any extended period of time, you may have some problem other than a weak module. At that point, you would probably need to take the cover off the battery and check for corrosion on the sensor wires or bus bars. Also, there are other possible non-hybrid battery causes for a red triangle. Check your dipstick to make sure your crankcase contains sufficient oil, use a multimeter to make sure your 12V battery is not discharged below 12 V, check the reservoir containing your inverter coolant to make sure it is circulating when the car is in Ready mode, and when the engine is cold, check your radiator to make sure it contains sufficient coolant for your ICE. It is likely that there is some problem with the HV battery, nonetheless, as indicated by the P3000 code you read. Possibly the device you are using is not seeing all of the hybrid codes. Most people who have taken their cars to Autozone to have the codes read also report that the code readers Autozone uses are similarly unable to read all of the hybrid codes.

 

I understand the reasons for your decision.

With the Prius being the spare car, a concern would be that unless it is driven regularly (for 15 min or more every two to three days) the GB battery will fail sooner rather than later. Please read all of the warranty information as there is a part in it that says (paraphrased) if the car sits for some period of time without being driven, it will void the warranty. The devil is in the details, so check the details carefully.

Good luck, I hope it lasts for as long as you need it.

 

Exactly. A used battery is the exact wrong choice for a vehicle that won't have its BMS turned on all the time. A used battery will last longest in a taxi where the car's inverter is basically on all the time. It will fail the earliest when it is a spare vehicle.

As to your original question, 30mOhm's is not abnormal or bad. BUUUUT, if it is too different than other modules then it's a problem. Usually you're fine up until about 50mOhm to 55mOhm.

 

As close to a dead short as you can possibly get is exactly what you want for battery series resistance.

Just think, if each block is 31 mΩ and there are 14 blocks, that's almost half an ohm total. Now put 80 amps in or out of that battery (about 16 kilowatts) and 3 kilowatts of that is going nowhere but resistive heat.

So yes ... the internal resistance figures are specified in small units.

 

I'm curious how well your reconditioned battery has worked out after using it a few years. My 2006 Toyota Highlander Hybrid battery at 193k miles still seems to work fine. I plan to DIY replace the hybrid battery whenever it finally gives out.