The car is a 2006 with 211,000 miles on it. Here's my symptoms: Fast recharge and discharge. 39 to 40 Mpg, used to be 44-50 Mpg A lag of energy at times. Higher RPMs than usual. I have no warning lights. I decided to take apart the battery case and I tested each battery, and to my surprise the batteries tested at 8.24 to 8.16 volts. There was no obvious bad cell, and the copper plates had little to no corrosion. The 12 Volt battery is at 12.6 Volts. I have the cells cooling off and are discharging hoping to just find a bad cell, otherwise I do not know where to look. Could it be the HV ECU?
Also, I was thinking about doing a battery swap with my Vehicle to see if I could troubleshoot that way too. I just am wondering if my inverter could damage the swapper battery.
If there are no warning lights on, then there are no diagnostic trouble codes. However if you want to monitor the traction battery module pair voltage under dynamic conditions, get Mini VCI. That will also be very helpful if/when fault codes are logged. Consider basics: when did you last replace the iridium spark plugs? What is the condition of the engine air filter? How frequently does the engine need oil to be added? Measure cylinder compression pressures by using Mini VCI and a compression gauge, to see how worn out the engine is.
