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What is a Granny Charger?

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February 27, 2024

A “granny charger” refers to a small, portable electric vehicle (EV) charger that plugs into a standard wall outlet. It provides slow trickle charging for EVs and is intended only for occasional emergency use, not as the primary charging method. The granny charger gets its nickname from the idea that you would use it to charge your EV when visiting granny’s house if she didn’t have a proper EV charging station. Let’s take a closer look at what granny chargers are, how they work, and how to use them safely.

What is a Granny Charger?

A granny charger, also known as an in-cable control box (ICCB), is a portable EV charger that comes standard with most new electric vehicles in the US. It consists of a charging unit built into the cable with a typical household plug on one end and a connector that plugs into your EV on the other end.

In the US, granny chargers have a standard NEMA 5-15 plug like you find in any home. They are limited to a maximum of 12 amps (2.9 kW) of power output to avoid overloading a typical 15 amp household circuit. The connector that plugs into the vehicle is usually the J1772 or Tesla connector.

a Granny Charger

Why is it Called a Granny Charger?

There are two main theories behind the granny charger nickname:

1. It charges slowly like a granny

A full charge from a granny cable can take over 24 hours, much slower than typical Level 2 or DC fast charging. The slow speed earned it the “granny” moniker.

2. It’s for charging at granny’s house

The idea is you would use the portable granny charger when visiting relatives, such as your grandmother, who don’t have an EV charging station available.

Intended Use of Granny Chargers

Granny chargers are intended for occasional emergency use only. Manufacturers include them with new EVs as a basic backup charging method when away from home and lacking access to better EV charging options. They are not designed for regular daily charging.

The slow charge speed of just 2-3 kW is the tradeoff for the convenience and portability of being able to plug into any standard wall outlet. While handy in a pinch, relying solely on granny charging would be extremely inconvenient for most drivers.

Pros and Cons of Granny Chargers


  • Convenient, portable charging anywhere there is a wall outlet
  • Provides basic charging in an emergency when no other options exist
  • Cables are typically lengthy, up to 25 feet, allowing access to distant outlets
  • Doesn’t require any special equipment other than a common household socket


  • Very slow charging speed – can take 24+ hours for a full charge
  • Not suitable for repeated daily use or as sole charging method
  • Risk of overloading and overheating household circuits if used improperly
  • Exposes wiring to outdoor elements if cable run through window etc.
  • Incompatible with electrical grids in other countries

How to Use a Granny Charger Safely

While granny chargers provide a convenient backup charging method, they must be used properly to avoid risks. Here are some tips for using a granny charger safely:

  • Use only occasionally – These are not designed for daily charging. Frequent use stresses electrical systems.
  • One socket only – Plug into a single wall socket without any other devices. Never use an extension cord.
  • Outdoor safety – Don’t run cords through windows or leave exposed outdoors. Use weatherproof outdoor sockets.
  • Ventilation – Ensure adequate air circulation around electrical outlets and charging cable.
  • Inspect cord – Check that the cable and plug are in good condition without damage or scorch marks.
  • Have electrician inspect socket – Ensure the electrical socket can handle 12A load over extended periods before using.
  • Use GFCI outlet – Connect granny charger through a ground-fault circuit interrupter (GFCI) outlet for safety.
  • Monitor charging – Stay nearby to monitor the charging process for any potential issues.
  • Unplug when done – Always unplug the granny charger from the wall outlet when finished charging.

Following these precautions will help minimize any risks and keep both you and your electrical system safe when using a granny charger. But again, it’s best to avoid using these cables regularly if possible.

Safer Charging Alternatives to Granny Chargers

For regular daily charging, there are safer and more convenient options than granny chargers:

Home Charging Station

A Level 2 EVSE installed by an electrician, providing faster and safer overnight charging. Smart options allow programming charge times to leverage cheaper overnight electric rates.

Public Charging Stations

DC fast chargers along major roadways for convenient top-ups while out and about. Though fees apply, charging is significantly faster than a granny cable.

Portable Charger

Portable Level 2 chargers on wheels offer 240V charging almost anywhere. They can plug into RV outlets and are a step up from granny chargers.

Solar Charging

Home solar panel systems with integrated EV charging allow for free daylight charging. Excess solar can be fed back to the grid for credit.

For most EV owners, relying solely on granny chargers would be highly impractical. Investing in proper home, workplace, or public charging solutions is key for enjoyable and convenient EV ownership.

Safety Hazards of Overusing Granny Chargers

Granny chargers are only designed for occasional emergency use. Using them as your primary charging method can be unsafe:

  • Fire risk from overheated wires, sockets, and circuit breakers
  • Electrical damage to fuses, circuits, and components
  • Shock/electrocution hazards from exposed wiring
  • Void EV warranty against charging system damage

The 2-3 kW capacity of a granny charger far exceeds typical household gadgets. Prolonged 12A power draw can overload a 15A household circuit. This can lead to overheating, arcing faults, and potentially fire.

Ensure your electrical system is inspected and suitable before attempting frequent use of a granny charger. Never leave it unattended.

Key Safety Tips

  • Use only occasionally as emergency backup
  • Have an electrician inspect socket suitability
  • Ensure adequate ventilation and air circulation
  • Use weatherproof outdoor sockets if outdoors
  • Connect through a GFCI outlet
  • Monitor charging to catch any issues
  • Unplug immediately if plug or cable hot

By following basic safety precautions, granny chargers can serve their intended purpose as an occasional charging solution when on the go. But for regular daily charging, invest in proper Level 2 or fast charge options for best performance and safety.


In summary, a “granny charger” is the informal term for the small portable EV charger that comes standard with most electric cars. It provides slow trickle charging by plugging into any common wall outlet. Granny chargers are intended only for emergency backup use, not daily charging. While convenient in a pinch, they have very slow charge times. Improperly using granny chargers as your primary charging method can overload electrical circuits and cause fire risks and damage. Follow basic safety tips such as using infrequently, inspecting the equipment, and monitoring charging to avoid issues. For regular use, invest in proper home or public charging stations for faster and safer charging.

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