This is a cross post from groups.yahoo<br><br>Trying to diagnose the power fall off around 70 mph the <br>tech "equalized the cells" in the battery. He could feel the drop <br>out/surging effect, but could see nothing on his scanner at those <br>times.<br><br>Afterwards it feels a little zippy-er in the 20 - 45 range. Anybody <br>else had experience with the application of this technique?<br><br>I heard it had been tried on another Prius when one of the motors <br>would not shut off. I don't know which.<br><br>Joe O'Laughlin

Cool, 'tis best to equalize the di-lithium<br>crystals before exceeding Warp 7...<br><br>Were you as lucky as I, to find a reputable service department within a 57 mile radius from home?<br><br>Peter, the most excellent Prius Tech @ Muller Toyota showed off the Toyota Hand Held Tester's ability to individually (in pairs) diagnose and treat battery modules.<br><br>Who's yr guy and dealership? Sounds like they've got the right stuff!<br><br>Jeff

I hope your Prius is back to running with normal power. However, it seems unfortunate (for your battery pack) that this "equalization" process was necessary at all. "Equalization" as it was described to you must be bringing each of the 38 individual modules that make up the battery pack to the same state of charge. Normally, a series connected battery pack is charged in series and the individual cells of which there are 228 in the Prius receive a series DC charge current. <br><br>However, if the capacity to store charge (or its ability to accept charge) is different from one module to another the state of charge can become significantly different from one module to another. The greatest potential to cause this problem will occur if the battery pack frequently gets a deep discharge before recharge (and the recharge is never really completed). In the worst conditions, the voltage on a module or individual cells will actually reverse during discharge of the battery pack. Comparing module voltages while the battery pack is being discharged will reveal if the state of charge among the modules is not "equal". This is probably what the Toyota dealer checked out when you got service. Having a low state of charge on just one or a few cells in the pack will cause the overall performance of the battery to "tank". It's like a chain with a weak link.<br><br>It has been my experience that continued "equalization" problems of this kind eventually lead to the replacement of the "worst cells". Once replaced, these now "new" cells can contribute to an ongoing problem since these cells will likely have greater charge capacity than the older cells in the pack. How many miles have you got on this car when your performance problems began? Any reason for unusual deep discharges of the battery pack? Or failure to get a good recharge?

Joe O'Laughlin said: "I heard it had been tried on another Prius when one of the motors <br>would not shut off. I don't know which."<br><br>The phrasing of this statement is needlessly alarming. The drive motor (aka motor/generator 2) would never exhibit this condition as it would create the unsafe condition of a car unwilling to stop. A battery pack that always reported a low charge could cause the THS to run the ENGINE all the time (no stealth mode) to keep trying to charge the battery through the GENERATOR (aka motor/generator 1). Try not to use the word "motor" when describing this condition. It's unnecessarily alarmist.<br><br>Also, it's best not to continue spreading rumors for which you don't have a source. At least you correctly identified it as a rumor.<br><br>Robert Snyder<br>NJ-PIKACHU

Thanks for your explanation.<br><br>The faltering/surging power effect at 70ish mph has been with me since the beginning. Recently it seemed to expand to 65 - 72 mph, which is when I began to worry.<br><br>I just had my 7500 mile service.<br><br>There has never been any tell tale evidence of deep discharging, etc. I "just drive it" at 50 mph up steep mountain roads, then in free fall back down. But can't help noticing the power fluctuations on freeways.<br><br>Joe O'Laughlin

Hi,<br><br>Depends on how new the car is--heard that most probs were with inadequate "dealer prep" which involves charging the 12V battery to a predetermined value, at which point the Prius is started and HV battery charge takes place.<br><br>The fact that the tech has direct access to individual module SOC TEMP ETC ETC ETC means that Toyo has complete control of the NiMH pack.<br><br>Jeff (experiencing random episodes of euphoria @ 21K.)