A pack is managed by its temperatures
A lithium-ion pack is charged, discharged and protected according to cell temperature, so every module carries thermistors, usually 10 kΩ NTC parts on cells and busbars. The battery management system reads each one through a resistor divider and an analogue-to-digital converter and converts the result with the curve of that part.
The curve matters. A 10 kΩ thermistor with β = 3435 K reads 4847 Ω at 45 °C and 2981 Ω at 60 °C by the Beta model. A part with β = 3950 K has the same 10 kΩ at 25 °C but a different resistance everywhere else, so software written for one reads wrong with the other, and the error grows toward the temperature limits where it matters most. The NTC calculator converts for any β and also fits Steinhart–Hart coefficients to three datasheet points, which follows a real part more closely than the Beta model over a wide range.
How finely the temperature is resolved depends on the divider and the converter. Because the thermistor is non-linear, the voltage change per degree is largest near the middle of the range and shrinks at both ends; the ADC resolution calculator gives the average resolution over a range, and the ends will be worse than that average.
Motors, inverters and charging connectors
Traction motors carry a PT1000 or NTC in the stator winding; a PT1000 reads 1573.25 Ω at 150 °C. DC fast-charging connectors monitor the temperature of their power contacts, commonly with PT1000 sensors, so that the charging current can be reduced before a poor contact overheats. These are two-wire sensors on a few metres of cable, where the lead resistance adds a small, constant error; the RTD lead-wire error calculator shows how small for a PT1000 and why a PT100 would be ten times worse.
Coolant pressure
Liquid-cooled packs and power electronics run at low pressure: 2.5 bar is 36.3 psi or 250 kPa. Automotive sensors are usually ratiometric, with an output that is a fraction of the 5 V supply rather than a 4–20 mA current. The pressure converter handles the units.
The factory: dew point, not relative humidity
Electrode coating, cell assembly and electrolyte filling take place in dry rooms, because the electrolyte salt reacts with water. Dry rooms are specified by dew point, typically −40 °C and lower. At 20 °C, a dew point of −40 °C is a relative humidity of under 1 %, a region where relative-humidity sensors are of little use and a dew-point transmitter is the instrument. The dew point calculator converts between dew point and relative humidity; its formula is valid down to a dew point of −45 °C, so the driest rooms are beyond its range.
Sealing and vibration tests
Packs and connectors are specified with IP ratings. IP67 is temporary immersion; high-pressure, high-temperature cleaning is IP69K, a separate test that IP67 does not include. The IP rating decoder explains the difference.
Vibration qualification profiles are written in g against frequency, while displacement limits of the shaker are in millimetres. The vibration converter converts between acceleration, velocity and displacement at one frequency.
Outside the scope of this site
Cell voltage measurement, pack current by shunt or Hall sensor, insulation monitoring and state-of-charge estimation are not covered here.
Updated October 11, 2026