With detailed data from OBDII (see this post) I've started thinking about ways to track the health of our HV batteries. But first, some of the data available from the Battery Energy Control Module (BECM) is:

__Battery Age__: Mine is 23 months - sounds right for car built in April 2013.__Battery voltage__: Runs about 282V. A 5 minute run gave min/max of 264V/303V.__Battery Current__: Varied from -114 amps (charge) to 94 amps (discharge). Limits (see below) should be about +/-120 amps.__Battery Temperature__: My 5 minute run had values from 62 to 66F (mid 30s OAT).__State of Charge (SOC)__: Both actual and displayed values in %. Fitting a straight line to the data gives: Actual SOC = 0.38545*(Displayed SOC) + 26.4%__Charge Limit__: Reads a constant 35000 watts. At 282 volts that's 124 amps.__Average Cell Voltage__: My min/average/max for this PID was 3.48/3.71/3.99 volts__Minimum Cell Voltage__: My min/average/max for this PID was 3.44/3.70/3.97 volts__Battery Cell Variation__: My min/average/max for this PID was 0.00/0.02/0.07 volts. On a statistical basis the % of times each value was registered was:

0.00=0.3% 0.01=58.8% 0.02=24.3% 0.03=10.1% 0.04=6.0% 0.05=0.4% 0.06=0.1% 0.07=0.02% (only once!)__SOC Module Variation__: Reads a constant 1.62% - not sure what this means. Will it go up?__In Car Temp__: Mine read 52 or 54 F the whole time (we Virginians are tough!). Of course this is probably the inlet cooling air, so with 30s outside and recirc heat likely on up front, the air reaching the battery could well be that cool (but then we don't sound so tough).__Fan Speed__: Read 0 during this run - I guess the HVB wasn't warm enough.

So back to health, here are some possibilities.

__Battery Cell Variation__: With age, this might go up. Right now I have a maximum of 0.07 volts. You must be careful though because the maximum values appear to depend on the maximum current. Will try and set up a "standardized" test where the battery is run through heavy charge/discharge cycles of, say, +/-100 to 120 amps.__Battery Cell Average & Minimum Voltage__: Might be useful but the above "variation" may be enough of an indicator.__Battery Resistance__: This value must be calculated. Using the average pack voltage, voltage variation with charge/discharge and battery current, the resistance of my battery appears to be about 0.10 to 0.15 ohms. Again the above test should give a more consistent value. Resistance may vary with SOC and temperature and is expected (?) to go up with time.__Battery Age__: For reference__Total Miles__: For reference (and maybe lifetime EV miles as well)

Sure wish I had numbers from when The Enterprise was new - and from other cars out there!