A charger in the supermarket car park sounds ideal: you do your shopping and the battery tops up in the meantime. Whether it actually gets you anywhere depends on the charger, how long you stay and what you need.
Which chargers are there?
Shops usually have two kinds. There are AC chargers, often 11 or 22 kW, and there are DC fast chargers. The power you actually get also depends on your car. Many cars charge more slowly on AC than the charger could deliver, so a 22 kW charger is not always twice as fast as an 11 kW one. The difference between the two is explained in AC vs DC charging.
What does a shopping trip give you?
Let’s do the sums. Say your car uses 18 kWh per 100 km and you spend 45 minutes in the shop:
- At an 11 kW AC charger you add 11 x 0.75 = 8.25 kWh. That is good for roughly 46 km.
- If your car can only take 7.4 kW on AC, it is 5.55 kWh. That is roughly 31 km.
- At a fast charger it depends on your car. If it charges for 20 minutes at an average of 60 kW, you get 20 kWh, roughly 110 km. That average is an assumption: power drops as the battery fills up, as you can read in the charging curve.
So with AC you cover about the day’s driving, not a long journey. That is exactly what a supermarket charger is good for: a bit of topping up while you are parked anyway.
What will you pay?
Tariffs differ per retail chain and per operator, and they can change. Sometimes charging is free for customers, often you pay. What applies today is shown on the charger or in the operator’s app.
A worked example with an invented tariff: say a kWh costs 0.50 euro. Then 10 kWh costs 5 euro. At home your kWh price is usually lower, so compare it with your own energy contract. You will find more figures in how much a charge costs.
Here is how to go about it.
- Read the tariff before you plug in.
- Check which payment methods or charging cards the charger accepts, so you are not stuck at the charger with an app that does not work.
- If charging is free, check whether there are conditions attached, such as a maximum duration. There is more on this in free charging: myth and reality.
Watch out for idle fees
Is your battery full but you are still at the checkout? Then a per-minute fee can start running. How high it is and after how many minutes it kicks in differs per operator.
An example with invented figures: say the idle fee is 0.10 euro per minute. If you stay another 15 minutes after charging, you pay an extra 1.50 euro for a charger that is no longer doing anything for you. With a long queue at the checkout it adds up faster than you think.
What helps:
- Set a notification in the app for when the session is finished, or stop the session yourself.
- Do not charge further than you need. For a top-up of 30 to 45 minutes, the battery does not have to be full.
- Read the charger’s terms before you start.
Everything about this fee is in how to avoid idle fees.
When it does not pay off
A shop charger is not always the best choice. Skip it in these situations:
- You have your own charger at home or at work and drive short distances. Then you hardly need the top-up.
- You are on a long trip. A fast charger along your route is a better stop than a car park where you stay for an hour.
- The charger is occupied or broken. Shop car parks can be busy, and a charger that does not work is no use to you. Do not count on it blindly, especially with a nearly empty battery. See what to do when a charger is occupied and what to do with a broken charger.
How to use them well
- Check the map beforehand to see whether the charger exists, what power it has and who the operator is.
- Plug in and check that the session has really started, on the screen or in the app.
- Note how long you expect to be away. That tells you whether an AC charger will do.
- Unplug as soon as you are done and move your car.
A charging bay is for people who are charging. Parking without charging blocks the spot for someone else, so keep charging etiquette in mind.
Which shops near you have a charger, and at what power, is shown on the map.