Session success measures whether drivers got energy. That makes it the most useful operational number a charging network can compute, and the definition is where most implementations go wrong.
Define the denominator carelessly and the metric either flatters the network or becomes unusably noisy.
What counts as an attempt
The reasonable definition is a deliberate action by a driver intended to start charging: presenting a card, a remote start, a payment authorisation, or connecting a cable at a unit configured to start automatically.
The unreasonable one is counting every connector state change, which includes people plugging in to check something, and produces a denominator full of events nobody intended as charging.
What counts as success
A transaction that delivered a meaningful quantity of energy. A session that started and stopped almost immediately delivered nothing useful and should not count as a success merely because a transaction record exists.
Setting a minimum threshold is necessary and slightly arbitrary. Documenting the choice matters more than which value is picked, because comparisons over time only mean something if the definition held constant.
Separate the failures you own
Reporting a single blended number hides which of these is moving. The split is what makes the metric actionable rather than descriptive.
- Charger faults, which are yours.
- Backend or platform failures, which are yours.
- Payment failures, which may be yours or a provider's.
- Vehicle-side refusals, which are not yours.
- Driver abandonment, which may indicate a usability problem that is yours.
Segment before drawing conclusions
A network-wide figure averages away everything useful. The same number by site, by hardware revision, by firmware build and by payment method is where the actionable pattern lives.
Concentration is the signal. A network at ninety-something percent overall may have a handful of sites doing far worse, and those are where the returning drivers are being lost.
Watch the trend, not the level
The absolute value depends on your definitions and is not comparable with anyone else's. The direction over time, with the definition held constant, is comparable with your own past and is what matters.
A step change usually follows a firmware release, a platform update or a payment provider change, which makes the metric useful as a regression detector.
Make someone own it
A metric computed and reported to nobody changes nothing. Session success needs an owner who investigates the worst-performing segment each period and closes the causes.
Without that, it becomes another number on a dashboard, which is where most operational metrics go to be ignored.