leafA cell-voltage chart can be the most informative screen in a Leaf app—and the easiest one to overinterpret. Ninety-six bars are a lot of detail. One bar sits lower, the spread turns a different colour, and suddenly an online “safe mV” threshold seems like a diagnosis. Slow down and put the reading back into its context.
What cell spread actually measures
Spread is simply the highest cell-pair voltage minus the lowest at that sample. If the highest is 3,905 mV and the lowest is 3,880 mV, the spread is 25 mV. The figure summarises the extremes; it does not tell you how the other 94 pairs are distributed or how long the difference lasted.
Leaf Pro shows the individual bars and a separate balance histogram for that reason. Tap the bar to identify the cell pair and read its value. Do not judge only by apparent bar height: a graph can magnify small differences so you can see them.
Why an idle and a loaded reading differ
Battery voltage changes under load. Charge state and temperature provide further context. A screenshot taken at rest after charging is not the same experiment as one taken while the vehicle is supplying power. Comparing them against a single universal cutoff discards information that matters.
When recording, preserve the pack current, SOC and temperature alongside the spread. You are trying to understand behaviour under conditions, not collect the largest number the screen can produce.
Look for a repeated pattern
A pair that repeatedly moves away from the pack under comparable conditions deserves more attention than one isolated sample. The useful question is whether the same part of the pack is consistently unusual, whether the behaviour persists, and whether it corresponds with an actual driving symptom.
Leaf Pro’s Full Assessment examines cell deviations across the session and distinguishes rest and load observations. It also reports coverage. Without sufficient cell data, a report cannot honestly make the same claim as a well-recorded session.
Why there is no universal pass number here
A threshold may belong to a particular service procedure, charge window, model or test method. Removing those conditions and posting the number as “all Leafs must be below this” changes its meaning. It can falsely reassure someone with an intermittent issue or alarm an owner whose measurement was made under different conditions.
The app’s voltage-loss inspection is a separate conditional check. Its eligibility note matters as much as its result. “Not run” is not “passed”, and a pass only concerns what was checked. Read the inspection guide if that is the result you are trying to interpret.
A sensible way to investigate
- Confirm the car and battery pack are correctly identified.
- Capture a normal recording with cell polling enabled.
- Start and stop the session while parked; drive legally and leave the phone alone.
- Review repeated cell behaviour alongside current, SOC and temperature.
- Take the recording to a qualified specialist if the pattern or vehicle symptoms raise concern.
What not to conclude
A balancing indicator does not prove capacity has been restored. A narrow idle spread does not guarantee good behaviour throughout a drive. A wide sample does not name the part that should be replaced. A phone app cannot determine the physical condition of every connection and component in a high-voltage pack.
Do not open the battery or attempt high-voltage repairs based on a chart. The value of the recording is that it gives a professional something concrete to investigate—and gives you a better question to ask.