How eMabler Measures EV Charging Success Rate
We measure Success Rate across every charging attempt and every charger in a network. That shows you which chargers hold your rate down and how much fixing them would raise it.
Authors
Calculation and methodology: Ville Parviainen, CTO & Co-founder, and Awais Amir, Senior Data & AI Engineer
Commercial analysis: Juha Stenberg, CEO & Co-founder
Last updated
85% sounds fine, until you put a price on the other 15%
Uptime tells you the charger is online. Success rate tells you whether the driver who plugged in got a charging session started. In a 2025 study of more than 100,000 sessions, chargers reported 98.7% to 99.9% uptime, yet only 71% of charging attempts succeeded. New stations averaged 85%.1
Here is what the gap between 85% and 97% costs in three businesses.
Retail: the charge fails, the customer drives on
A retail chain with 4,000 charge points and 800,000 charging attempts a month. Average session value €10.
The gap: €960,000 every month. €11.5 million a year.
The larger cost is inside the store. 44.5% of EV drivers buy something while they charge, spending about €35.2 If half of the drivers whose charge fails go elsewhere, Retailer B also loses €748,000 in store sales every month.
Then come the drivers who don’t return, the one-star reviews and the calls to your help desk.
| Retailer A | Retailer B | |
|---|---|---|
| Success rate | 97% | 85% |
| Failed charges / month | 24,000 | 120,000 |
| Charging revenue at risk / month | €240,000 | €1,200,000 |
Parking: no charge, no parking fee
A parking operator with 10,000 charge points in city garages and 400,000 charging attempts a month. Average charging session €9.
The gap: €432,000 every month. €5.2 million a year.
A driver who can’t charge often drives to the next garage, and the parking fee leaves with them. If 3 in 10 do, at an €8 fee, Operator B loses another €115,000 a month in parking revenue.
Add bays blocked by cars that never charged, intercom calls at the exit and reviews that name your garage.
| Operator A | Operator B | |
|---|---|---|
| Success rate | 97% | 85% |
| Failed charges / month | 12,000 | 60,000 |
| Charging revenue at risk / month | €108,000 | €540,000 |
Energy retail: the failure shows up at 7 a.m.
An energy company with 50,000 home chargers sold together with an electricity contract. Each household charges every third day, about 10 times a month.
At home there is no other charger to try. The driver finds out in the morning, when the car they need is still empty.
The lost kWh are the small part. The contract is the big one.
Switching supplier takes minutes, and nearly 1 in 3 European consumers have done it in the past two years.3 If Company B loses 5% of its EV households a year to charging problems and Company A loses 1%, B loses 2,000 more households every year. At €800 per household (margin over the contract plus the cost of winning a replacement), that is €1.6 million a year in lost customers.
€3.0 million a year in total.
And when the charger fails, the household calls you, not the charger manufacturer.
| Energy company A | Energy company B | |
|---|---|---|
| Success rate | 97% | 85% |
| A household wakes up to an uncharged car | about once every 3 months | every 3 weeks |
| Electricity sales at risk / month | €30,000 | €150,000 |
Illustrative examples. “At risk” means gross value before drivers who retry and succeed.
- 1 ChargerHelp, 2025 EV Charging Reliability Report, September 2025. US data, 100,000+ sessions on 2,400 chargers.
- 2 Hardman, UC Institute of Transportation Studies, June 2026. Average spend $39.82, about €35.
- 3 Eurelectric and Accenture consumer survey 2024, 12 European countries.
Measuring success starts with the charging attempt
eMabler measures Success Rate as the share of charging attempts that lead to a started charging session, across every charger in a network.
Success Rate (G) = Σ successful attempts in G ÷ Σ attempts in G
G is any group of sockets: a charger, site, network, charger model, firmware version or manufacturer, over any period.
Success rate stands or falls on recognizing a real charging attempt, and charger data makes that hard. A charger reports what it does as a stream of signals, so one plug-in can produce many of them, and a faulty unit can send them with no driver there at all.
eMabler's method recognizes the real attempts in that noise and counts one plug-in as one attempt, however many signals the charger sends. That precision lets us include every charger, even the ones that rarely or never start a session. Those are the chargers where drivers are let down, so they belong in your success rate.
What counts as a charging attempt
There is no agreed definition of success rate yet, and a single choice about what counts can change the figure substantially. A success rate is only useful if it is built on parameters tested against real charger data, shows you which chargers let drivers down and tells you what to act on first. So here is how eMabler's Success Rate calculation handles what happens at the charger every day.
Several cards, one plug-in
A driver tries several cards before one works, without unplugging. That is one attempt, and it counts as a success.
Nothing starts
A driver plugs in and leaves because charging never starts. That is one attempt, and it counts as a failure.
Nobody at the charger
A faulty charger sends signals that no driver could cause. None of those signals is an attempt, so the noise stays out of your success rate.
A charger that stays silent
Some chargers report nothing until a driver authorizes. When charging starts there, the session itself opens the attempt, so the visit still counts.
A success rate is only useful if it works like a map, showing which chargers fail drivers and where to act first. eMabler's Success Rate is built on rules tested against real charger data, so you can trust the map.”
What counts as a successful attempt
An attempt succeeds when a charging session starts within it. The session record is the proof, so every success can be traced and billed.
A recorded session
The charger starts a session and the platform records it. A charger that reports charging without registering a session counts as a failure.
No time limit
A driver who plugs in and starts charging from an app minutes later still succeeds.
Every start counts the same
Cards, apps, roaming and chargers that start on plug-in all follow the same rules.
Counted the moment it starts
An attempt counts as a success as soon as its session starts, without waiting for the driver to unplug.
Pauses stay in the attempt
When the car or the charger pauses charging, the attempt carries on, so a pause doesn't count against your rate.
Overnight sessions
A session that runs overnight counts as a success on the day the driver plugged in, so each day's rate stays accurate.
How to calculate success rate
Divide the charging attempts that led to a started session by all charging attempts. The division is the easy part. The result is only as reliable as the attempt count behind it: you first have to pin down what counts as an attempt, then track each one through the stream of signals a charger sends. eMabler's calculation does both with only the data every OCPP charger already sends to its charging platform, so it works on any OCPP hardware.
Both chargers have the same number of attempts, so the combined rate sits exactly halfway between the two. If one charger were busier, the combined rate would move toward its rate, because every attempt counts the same.
What to look for in a success rate
Providers still define attempts and successes in different ways, so two networks with the same figure can offer drivers very different experiences. Before you compare a success rate or act on it, check how it was built.
eMabler's Success Rate meets every one of these checks.
It starts at the plug-in
When the charger reports the plug-in, a visit where charging never starts counts as a failure.
It counts every charger
Signals that no driver could cause are filtered out first, so no charger has to be left out to keep the figure stable.
It points to the charger and the failure category
Every failed attempt carries its charger and its failure category, so you know where to start.
It confirms the session
Success needs a recorded session. A status that only looks like charging doesn't count.
It uses one set of rules everywhere
The same rules apply to every network, manufacturer and month, so figures stay comparable.
Count every attempt on every charger, and you see how much of the drivers' experience depends on a small number of units. When that's the case, those are the units to fix first.”
How charging attempts fail
Every failed attempt ends in one failure category, and each category points to a different place to look first. That turns a low success rate into a list of places to check.
Unplugged quickly
Look first at card readers, the app flow and signage at the site.
Unplugged after a short wait
Look first at the card, app or roaming authorization flow.
Unplugged after a long wait
Look first at load management, scheduling and the back-end response.
Charger fault
Look first at the charger's hardware and firmware.
Power without a session
Look first at the charger's configuration. Billing is affected.
eMabler's Managed Services takes the daily running of your charging network off your team.
See Managed ServicesFind the chargers that hold your rate down
You see your success rate for the whole network and for each charger. Read together, they show where your failed attempts come from and how much fixing the chargers behind them would raise your rate. That tells you whether to fix a few units or look across the whole network.
The same view shows how hardware performs in the field, because chargers that look identical can behave very differently once drivers use them.
Fix a few units
When a few chargers cause most of your failed attempts, start with them. Fixing a handful of units is the fastest way to raise your rate.
Look across the whole network
When failures spread across the fleet, the cause usually sits outside any single charger. A pattern like that needs deeper analysis.
Track your success rate in Data Insights
eMabler's Data Insights shows you your success rate for the whole network, site by site and charger by charger, next to socket availability, utilization, energy consumption and recurring errors. You see where your failed attempts come from day by day, with no exports and no waiting for a monthly report.
Explore Data InsightseMabler's promise is EV charging that just works, and our mission is to make EV charging invisible for EV drivers. Success Rate is how we make both come true.”
Success Rate decides the winners
Once a year, the eMabler Awards recognize the most reliable EV charging operators and hardware manufacturers, measured on Success Rate on the eMabler platform. The ceremony is on 26 November 2026.
Join the 2026 ceremony
Common questions about EV charging success rate
What is EV charging success rate?
Success rate is the share of charging attempts that lead to a started charging session. eMabler measures it across every charger in a network, so it shows whether drivers who plug in get a charging session started.
How is success rate different from uptime?
Uptime tells you a charger was online. Success rate tells you whether a driver who plugged in was able to charge. The two can tell different stories, because a charger can be online all day and still fail the drivers who use it.
How does eMabler calculate Success Rate?
eMabler divides the charging attempts that led to a started charging session by all charging attempts. For a site, a network or a charger model, it adds up the attempts and successes of every charger in the group first, then divides, so every attempt counts equally. The calculation uses only the data every OCPP charger already sends to its charging platform.
Which chargers does eMabler's Success Rate include?
Every charger in the network, including the ones that rarely or never start a session. Those are the chargers where drivers are let down, so they belong in the rate.
What counts as a charging attempt?
One plug-in by a driver is one charging attempt. It counts once, however many signals the charger sends, and signals that no driver could cause stay out of the rate.
What counts as a successful charging attempt?
An attempt succeeds when a charging session starts within it and the platform records it. A charger that reports charging without registering a session counts as a failure.
Why do charging attempts fail?
Every failed attempt ends in one failure category: the driver unplugs quickly, after a short wait or after a long wait, the charger reports a fault, or it reports charging without registering a session. Each category points to a different place to look first.
How can operators raise their success rate?
Start with the chargers that hold the rate down. When a few units cause most of the failed attempts, fixing them is the fastest way to raise the rate. When failures spread across the network, the cause usually sits outside any single charger and needs deeper analysis. eMabler's Managed Services helps with both: it finds and fixes recurring faults before a driver notices, and its team works through the results with you.
Where can I track my success rate?
In eMabler's Data Insights, for the whole network, site by site and charger by charger.