Power / Charging Speed
How quickly can the equipment deliver energy?
Mobile EV Charging Basics
Understand the key terms, how EV charging works, and what matters when choosing mobile charging equipment.
1 Four Things That Matter
When evaluating mobile EV charging equipment, there are four key factors. They are all connected, and there are tradeoffs.
Capacity
How much energy can the system deliver before it needs fuel or recharging?
Cost
What does the equipment cost to buy and operate?
Portability
How practical is it to move, load, unload and use roadside?
2 kW vs. kWh — Power vs. Energy
- kW (power level): how much energy the charger can deliver right now.
- kWh (energy): the amount of energy stored in the battery, like gallons in a tank.
- Speed: higher power levels add more kWh in less time. Level 1 (1–2 kW) is slower, Level 2 (3–19 kW) is faster, and DC fast charging (30–350 kW) is much faster.
3 The Three Main Charging Levels
EVs can be charged at different power levels. Each level is used for different situations.
| Level 1 (AC) | Level 2 (AC) | DC Fast Charging (DC) | |
|---|---|---|---|
| Typical supply | 120 V AC | 208/240 V AC | High-voltage DC |
| Typical power | ~1–2 kW | ~3–19 kW | ~30 kW to 350+ kW |
| Relative speed | Slow | Faster | Fastest (potential) |
| Typical use | Home (long dwell) | Home, commercial, workplace | Highway, commercial, fleet |
4 Power / Charging Speed — The EV Is the Boss
The charger offers a maximum available power, but the EV decides how much it will actually accept at any moment. Charging speed can vary based on battery state of charge, battery temperature, vehicle limitations and ambient conditions.
- Battery state of charge (for example, near 0% charges slowly)
- Battery temperature (very hot or very cold can reduce speed)
- Vehicle and battery limitations (software, battery chemistry, etc.)
- Ambient conditions (weather, etc.)
An EV near 0% may initially limit charging power to protect the battery — especially when it is very hot or very cold. A high-speed DC charger can also charge slowly under these conditions because the EV, not the charger, controls how much power it accepts.
Clean Power Matters
Inverter generator (clean power)
Low total harmonic distortion (THD). Smooth, stable power that is ideal for EV charging. EVroadHERO’s inverter delivers THD below 3%.
Conventional generator (“dirty” power)
Higher THD can cause charging problems or prevent charging.
THD = Total Harmonic Distortion. A lower THD means a cleaner, smoother waveform. Conventional generators can have much higher THD, which can cause issues with sensitive onboard EV chargers and other controlled equipment.
Typical Charging Speed Examples*
| Charger power | Estimated time to add 5–10 miles | Typical use |
|---|---|---|
| 9 kW (Level 2) | ~20 minutes | Mobile rescue charging (EVroadHERO) |
| 11.5 kW (Level 2) | ~15 minutes | Higher-power Level 2 |
| 30 kW (DC fast) | ~5–10 minutes | Mobile or public DC |
| 60 kW (DC fast) | ~3–5 minutes | Higher-power DC |
*Estimated time to add 5–10 miles of range assumes a typical EV (for example, a Tesla Model 3/Y), normal ambient conditions, and that the EV accepts the full charger output.
5 Capacity — How Much Energy Can You Deliver?
Mobile charging systems store or supply energy in different ways.
Generator-powered (Level 2)
- Runs on an engine (gasoline, or propane on some models)
- Refuel in minutes
- Rugged and proven
- Effectively unlimited capacity as long as fuel is available
- Typically used for Level 2 mobile charging
Battery-powered (DC fast)
- Large onboard battery (for example, 30–120 kWh)
- Finite capacity before recharging
- Can be recharged by a generator or the grid
- Much higher cost and larger size
- Used for mobile DC fast charging
60 kWh capacity example
A 60 kWh mobile DC system can deliver roughly 90% of a Chevrolet Bolt EV’s battery (66 kWh), providing a meaningful boost when drivers need it most.
6 Cost — A Wide Range
Equipment cost increases significantly with higher power and capacity.
Level 2 mobile (for example, EVroadHERO)~$5,500(typically under $10,000)
Mobile DC fast charging (battery-powered)Tens of thousands to well over $100,000
Mobile DC (generator-powered)Can exceed $100,000(depending on power and capacity)
7 Portability — Size and Weight Matter
More power and more capacity usually mean larger, heavier equipment.
Level 2 mobile (for example, EVroadHERO)
- Compact
- Wheels and handles
- Fits in a van or truck
- Designed for roadside use
High-power DC
- Much larger and heavier
- May require a trailer or large truck
- Can occupy a large portion of a bed or pickup bed
- More complex setup
Next steps: convenience charging
Now that you understand the basics, learn how rescue charging and convenience charging differ, and which type of equipment is right for your situation.