A granny charger takes a long time to charge an EV: at Level 1 speeds of about 1 kW, it adds roughly 2–5 miles of range per hour, so adding 10 kWh takes about 10 hours and a large battery can take well over a day from empty. In practice, granny charging works as an overnight top-up, not as a way to refill a big battery quickly.
Key Takeaways
- At about 1 kW, a granny charger adds roughly 2–5 miles of range per hour.
- Adding 10 kWh takes about 10 hours, so plan around overnight top-ups.
- A large battery can take well over a day from empty at Level 1 speeds.
- Level 2 charging at 7–19 kW is the practical upgrade for daily high mileage.
The Numbers Behind Granny Charging Times
The U.S. Department of Transportation puts Level 1 charging at about 1 kW, adding 2–5 miles of range per hour. A granny charger in the UK plugs into a standard 3-pin socket and works in the same slow Level 1 class, which is why drivers treat it as a backup or stopgap. Our guide to charging an electric car from a normal socket explains when that speed is acceptable and when it is not.
| What you add | At about 1 kW | Typical use |
|---|---|---|
| 5 kWh (roughly 15–20 miles) | About 5 hours | A short evening top-up |
| 10 kWh (roughly 30–40 miles) | About 10 hours | An overnight charge for a daily commute |
| 20 kWh | About 20 hours | A full day plugged in |
| 40 kWh battery, empty to full | Roughly 40 hours | Not realistic as a routine |
These are simple divisions of energy by power, before charging losses. Your car’s actual speed depends on the socket, the cable’s current limit and the car’s onboard charger, as our comparison of Level 1 vs Level 2 vs DC fast charging shows.
Why Partial Top-Ups Are the Realistic Use
Most drivers do not arrive home with an empty battery. If you drive 30 miles a day and plug in for 10 hours overnight, a granny charger roughly replaces what you used, and the battery level stays in a comfortable band. The maths only breaks down after long trips, when several days of slow charging may be needed to catch up. Drivers who rely on this pattern often ask whether they can leave a Level 1 charger plugged in all the time; the linked guide covers that habit in detail.
- Works well: low daily mileage, long parking time at home, a second car for long trips.
- Works badly: high daily mileage, a large battery, or only a few hours parked at home.
- Watch out: a socket used for hours at full load should be in good condition, and a dedicated circuit is the safer long-term setup.
How a Granny Charger Compares With Level 2
A dedicated Level 2 charger delivers 7–19 kW, adding about 10–20 miles of range per hour on U.S. DOT figures, so the same 10 kWh top-up takes roughly an hour instead of overnight. That gap is why most regular EV drivers eventually install a wallbox and keep the granny cable for travel and emergencies. If you are weighing that step, see how portable chargers depend on the outlet for what a portable unit can and cannot do on different sockets.
A Faster Portable Option
If a full wallbox install is not possible yet, a portable charger that can use a higher-rated supply is a middle step. The EV-ACS3210E 32A Type 2 portable charger delivers about 7 kW single-phase where the supply supports it and is IP66 rated; on a standard socket it still runs at socket speed, so check your supply before expecting the higher rate.
Frequently Asked Questions
How long does a granny charger take to charge from empty?
At about 1 kW, a 40 kWh battery needs roughly 40 hours from empty, and a larger battery takes proportionally longer. That is why granny charging is normally used for partial top-ups rather than empty-to-full charging.
How much range does a granny charger add overnight?
Over 10 hours, expect roughly 20–50 miles of range on U.S. DOT Level 1 figures of 2–5 miles per hour. Efficient cars on a healthy socket land at the top of that range; cold weather and losses pull it down.
How long do granny chargers last?
That is a lifespan question, not a charging-time question. A quality portable charger used within its ratings and kept dry at the connector should last for years of regular use; damaged plugs, overheated sockets and water in the connector are what usually end a cable’s life early. For the hardware side, see how long home EV chargers last.
Related Reading
- Can I Charge an Electric Car From a Normal Socket?
- Level 1 vs Level 2 vs DC Fast Charging: A Practical Comparison
- Can I Leave a Level 1 Charger Plugged In All the Time?
- Do Portable EV Chargers Work? How Speed Depends on the Outlet
