Fleets Don't Want to Build Fixed Charging Stations for Infrequent Needs: Can Door Energy's Mobile Charging Stations Be a More Flexible Backup Solution?

Fleet electrification doesn't mean all charging needs can be accurately predicted.

Ideally, vehicles travel along fixed routes daily and return to the same depot at night. Operators only need to build fixed charging facilities based on average daily mileage, parking time, and vehicle numbers. However, in reality, issues arise such as fixed charging equipment failures, unexpected additional transport tasks, vehicles missing nighttime charging, depot power outages, and remote locations lacking grid access.

These needs may only occur a few times a month, but can directly lead to vehicle downtime. Building a separate fixed charging facility to cope with low-frequency events not only incurs equipment costs for the fleet but may also require transformer expansion, cable laying, ground excavation, and power approvals. Even after the equipment is operational, if it remains idle for extended periods, the unit charging cost will continue to rise.

In this context, the Door Energy Mobile EV Charger, equipped with an energy storage system, offers an alternative approach: pre-storing electrical energy within the device and deploying it to parking lots, roadside assistance points, construction sites, or temporary work areas when vehicles require charging.

For charging stations with stable demand, it's not a complete replacement for fixed charging facilities; however, for fleets with infrequent demand, scattered locations, or unstable power access, Door Energy can be a more flexible backup asset.

I. Why are fleets' occasional charging needs becoming increasingly difficult to ignore?

Global EV growth is increasing the importance of backup charging

International Energy Agency data shows that global electric vehicle sales will exceed 20 million units in 2025, accounting for approximately 25% of global new car sales that year. In the same year, the total number of public charging points worldwide will exceed 7 million, and the number of fast and ultra-fast charging devices will increase from approximately 1.5 million in 2024 to 2.2 million.

While the public network continues to expand, the core issue for fleets is usually not "whether there are charging stations nearby," but rather whether vehicles can complete their tasks at the designated time and location. For example, if a logistics vehicle runs out of battery before returning to the depot, it cannot reach the charging station on its own, even if there is one 20 kilometers away.

What Fleets Need to Manage is "Abnormal Load"

Traditional charging planning mainly focuses on average daily electricity consumption. However, what truly determines the reliability of a fleet's service is often abnormal demand that exceeds the average.

Common scenarios include:

* Vehicles consuming power prematurely due to added routes;

* Drivers missing planned charging windows;

* Fixed charging equipment malfunctions, preventing vehicles from recharging on time;

* Power outages or rationing at charging stations, affecting the next day's service;

* New EVs have been delivered, but the fixed infrastructure is not yet complete;

* Vehicles are temporarily relocated to warehouses or construction sites without charging facilities;

* Low temperatures, high loads, or complex road conditions lead to actual energy consumption exceeding predictions;

* Multiple vehicles returning to the charging station simultaneously, causing short-term power demand to exceed the distribution capacity.

Therefore, fleets should not only ask "How much electricity do we need each day?" but also, "If the existing charging system suddenly becomes unavailable, do we have a second energy source?"

II. Why Low-Frequency Demand May Not Be Suitable for Fixed Charging Stations?

The Economics of Fixed Infrastructure Depends on Utilization Rate Fixed charging infrastructure is suitable for scenarios with concentrated vehicles, fixed parking locations, and stable charging demand. The longer the equipment is used each day, the easier it is to amortize the initial investment.

Conversely, if a fleet only installs a single high-power stationary charging unit for occasional weekly recharging trips, the charging infrastructure may remain idle for extended periods. Besides the charging equipment itself, operators may also incur costs for design, construction, permits, cabling, distribution cabinets, transformers, and electricity demand.

The U.S. National Renewable Energy Laboratory, in its fleet charging research, points out that high utilization rates are crucial for amortizing investment in charging infrastructure. Furthermore, electricity demand costs also need to be incorporated into the business model of high-power charging projects.

Mobile charging infrastructure isn't the optimal solution for all scenarios.

If 100 electric vehicles return to the same charging station daily, requiring thousands of kWh of electricity each day, stationary charging facilities typically remain the primary solution. This is because large-scale, continuous charging operations improve the utilization rate of charging stations and power distribution infrastructure.

Door Energy Mobile EV Chargers are better suited for the following needs:

Therefore, a more realistic architecture is usually "fixed charging + mobile charging". Fixed facilities handle the daily basic load, while Door Energy Mobile EV Chargers handle faults, peak periods, remote locations, and emergency tasks.

III. What capabilities does the 420kWh Mobile EV Charger offer?

It's a transportable, high-capacity energy storage and charging system.

The Door Energy MCP-E is a Mobile EV Charger integrating 420kWh energy storage, DC fast charging, and AC power supply. The device can be integrated with suitable transport vehicles or platforms and deployed to fleet depots, roadside assistance areas, or industrial sites, depending on the mission.

It is not a typical portable charging device, nor is it an autonomous charging robot. Its primary value lies in bringing large-capacity electrical energy to locations inaccessible by fixed charging infrastructure.

Actual project configurations still need to be confirmed based on the vehicle, transportation platform, local regulations, and application environment.

420kW is the total power of the four charging guns, not 420kW per gun.

This point must be clarified in the article. The equipment is configured with four charging guns, but 420kW is the total system output capacity and needs to be dynamically allocated among the four interfaces.

For example, when four vehicles are charging simultaneously, the system can allocate output based on each vehicle's maximum received power, SOC, and task priority.

The above are just examples of power dispatching; not all vehicles can receive the corresponding power. Actual output will also be limited by the vehicle's BMS, battery voltage, SOC, temperature, charging current, and equipment control strategies.

AC Output Expands Equipment Usability

In addition to providing DC charging for EVs, Door Energy can also support electric excavators, water pumps, lighting, or other industrial loads via AC output. Therefore, fleets do not need to rely solely on vehicle charging frequency to improve asset utilization. For example, the equipment can serve as temporary power at construction sites during the day and provide supplemental power to engineering vehicles at night. During the off-season for roadside assistance, it can also be deployed to outdoor construction sites, emergency lighting, or temporary work areas.

However, the load starting current, continuous power, power factor, and equipment interface still need to be checked in advance. A 200kW rated AC output does not mean that any 200kW load can be started directly.

IV. How many vehicles can a 420kWh capacity provide supplemental power for?

Nominal capacity does not mean that all of it can be output to vehicles

420kWh is the nominal energy storage capacity of the equipment. In actual operation, fleets typically do not completely discharge the equipment to 0%; conversion losses, low SOC protection, temperature effects, and emergency reserves must also be considered.

Assumptions:

* Nominal capacity is 420kWh;

* 10% minimum safe capacity is reserved;

* Overall charging, discharging, and conversion efficiency is estimated at 90%.

Therefore, the planned available power capacity for the vehicle is approximately:

420kWh × 90% × 90% = 340.2kWh

This is not a fixed commitment for the product, but rather a relatively conservative operational planning method. Formal calculations should use the confirmed available capacity and system efficiency after project verification.

Theoretical Number of Tasks Under Different Recharge Targets

Roadside assistance typically doesn't aim to charge a vehicle from 0% to 100%, but rather to replenish enough power to allow the vehicle to safely reach a depot, public charging point, or complete the remaining route. This increases the number of tasks a single Mobile EV Charger can handle daily.

How to calculate required capacity based on fleet data?

Operators can use the following formula:

Daily Energy Storage Requirement = Number of Affected Vehicles × Target Replenishment Capacity per Vehicle ÷ Overall Efficiency × Safety Factor

Assuming a fleet expects to handle 6 abnormal vehicles daily, with an average replenishment of 35kWh per vehicle, an overall efficiency of 90%, and a 15% allowance for demand fluctuations:

6 × 35 ÷ 0.90 × 1.15 ≈ 268kWh

In this scenario, a 420kWh system provides ample capacity margin. Even if some vehicles receive more replenishment than planned, the equipment is less likely to immediately enter a low SOC state.

Therefore, when choosing a Mobile EV Charger, one cannot only look at the maximum power. Capacity determines how many vehicles the device can continuously serve, while power determines how long each vehicle requires the device to operate for.

V. How much can a 420kW power output reduce rescue time?

First, distinguish between peak power and average effective power

420kW is the maximum output capacity of the system's four charging guns combined. However, a vehicle typically does not maintain peak power throughout the entire charging process.

Charging power gradually decreases as SOC rises, battery temperature changes, or the BMS activates protection. Therefore, the scheduling plan should use the average effective power, rather than simply calculating all tasks using 420kW.

The data in the table are theoretical values of "energy ÷ average power" and do not include equipment scheduling, on-site inspection, charging gun connection, communication handshake, and power reduction time in the later stages of charging. Therefore, it's inappropriate to directly claim that "most vehicles are fully charged within 30 minutes." A more accurate statement is: provided the vehicles are compatible and allow for higher power, the 420kW total output can reduce waiting times for multiple vehicles charging concurrently and for larger vehicles.

Four-gun design suitable for peak fleet tasks

A single-gun device can only handle one vehicle at a time. Even with high output power, other vehicles still need to queue.

The Door Energy four-gun Mobile EV Charger can allocate power based on task priority. For example, a vehicle about to depart can receive higher power, while three other vehicles that have been parked for a longer period can receive lower power.

This dynamic allocation method improves equipment turnover and reduces situations where "low-priority vehicles occupy all power".

Equipment self-recharge determines continuous operation capability

Depending on project conditions, equipment can restore its own power through DC or AC input. Door Energy provides the following charging references:

The 1 hour and 2 hours mentioned here refer to the charging time of the 420kWh Mobile EV Charger itself, not the charging time for all electric vehicles. Actual time will be affected by input power, battery temperature, SOC, efficiency, and power limitations.

VI. Which fleets are more suitable to use mobile charging as a backup solution?

Scenario 1: Multiple fleet sites sharing one set of equipment

If a company has three warehouses, each with only one or two temporary charging needs per week, building separate fixed fast charging facilities for each location may result in redundant investment.

A single Mobile EV Charger can be centrally managed by a dispatch center and deployed to different sites according to vehicle schedules. This way, the 420kWh energy storage capacity and 420kW charging capacity are no longer locked to a single address.

Scenario Two: Transition Period Before Fixed Infrastructure Expansion

Power expansion often involves load assessment, engineering design, permitting, equipment procurement, and construction. Meanwhile, newly purchased electric vehicles may have already been delivered.

Door Energy mobile charging can provide temporary charging capacity before expansion is complete. Fleets can also use this time to collect real-world route, energy consumption, and charging data, avoiding infrastructure construction based on overly optimistic forecasts.

Technical data from the U.S. Department of Energy indicates that, with proper design, buffered fast charging can reduce the required grid service capacity by approximately 50% to 80%. However, the actual reduction depends on the load curve, energy storage capacity, and replenishment strategy.

Scenario Three: Roadside Assistance and Remote Area Recharge

When vehicles are stranded far from charging facilities due to low battery, towing is not the only option. The rescue center can deploy charging equipment near the vehicle to replenish it with 10–60 kWh of power, restoring its driving capability.

In this scenario, CCS1 and CCS2 help cover vehicles from different markets; the 200–1000Vdc output range supports different voltage platforms. Meanwhile, the OCPP 1.6J can record mission time, output power, equipment status, and charging results.

However, if the vehicle is involved in a collision, flooding, high-voltage system failure, or 12V battery failure, rescue personnel should first perform fault diagnosis. Insufficient battery power and vehicle electrical faults cannot be handled using the same methods.

Scenario Four: Construction, Mining, and Outdoor Industrial Scenarios

Some construction sites lack a stable power grid, or the power capacity is only sufficient for infrastructure operation. In this case, the Door Energy Mobile EV Charger can not only charge electric construction vehicles but also support loads such as water pumps, lighting, and electric excavators via AC output.

If the equipment simultaneously handles EV charging and industrial power supply, the operator must reserve a minimum SOC to avoid the inability to perform emergency vehicle assistance after the industrial load consumes all the power.

VII. How to Assess Economics and Develop a Deployment Plan?

Don't Just Compare Equipment Purchase Prices

Determining whether a Mobile EV Charger is a worthwhile investment requires comparing the entire lifecycle cost, not just the equipment price.

The cost of a fixed charging project includes the charging piles, transformers, distribution cabinets, cables, ground construction, design, approvals, and electricity demand costs. Mobile charging and energy storage projects require consideration of equipment, transportation platforms, energy loss, dispatching, insurance, and regular maintenance.

Calculate using actual business data, not intuition

Assuming a fleet of 120 EVs experiences 6 abnormal charging incidents per week, each requiring an average of 35kWh:

Annual Abnormal Charging Amount = 6 × 35 × 52 = 10,920kWh

If a dedicated 420kW stationary unit is built for these abnormal demands, its theoretical annual output capacity is:

420kW × 8,760 hours = 3,679,200 kWh

Based solely on abnormal power replenishment, the equipment power utilization rate is approximately:

10,920 ÷ 3,679,200 × 100% ≈ 0.30%

This does not mean that mobile devices inherently have higher utilization rates. The key difference lies in the fact that mobile energy storage and charging stations can serve multiple sites and undertake tasks such as roadside assistance, power outage backup, and industrial power supply, thereby expanding their application scope.

Recommended Four-Phase Deployment Approach

The fleet should focus on monitoring the following KPIs:

* Number of charging tasks completed per month;

* Average output power per task;

* Average scheduling time from request to arrival;

* Charging connection success rate;

* Average remaining equipment SOC;

* Number of towings avoided per month;

* Reduction in vehicle downtime;

* Concurrent utilization rate of the four charging guns;

* Ratio of DC and AC charging;

* Ratio of EV charging to industrial power supply.

Conclusion: It's More Like a Fleet's "Mobile Energy Reserve"

The most important value of the Door Energy 420kWh Mobile EV Charger is not replacing all fixed charging stations, but rather freeing up energy storage, fast charging, and industrial power supply capabilities from fixed locations.

For charging stations with stable daily charging needs, fixed facilities should still handle the basic load. However, when demand is low-frequency, dispersed, temporary, and emergency-oriented, building multiple fixed charging stations may result in long-term idle power capacity and equipment.

Door Energy's 420kWh mobile charging system is equipped with four charging guns, with a maximum total DC output of 420kW, and supports CCS1, CCS2, and OCPP 1.6J. Simultaneously, the 200kW AC output can be extended to industrial loads such as electric excavators, water pumps, and lighting.

Therefore, a more robust fleet energy architecture is: fixed charging handles daily tasks, while the Mobile EV Charger handles abnormal loads, temporary capacity expansion, roadside assistance, and power outage backup.

FAQ

Q1: How to determine if a fleet should purchase mobile charging equipment? A1: At least 4–8 weeks of abnormal charging data should be collected, including the number of tasks, the amount of electricity charged per charge, the location of the incident, downtime losses, towing fees, and fixed infrastructure construction costs. If the demand is infrequent but dispersed, and there are simultaneous needs for roadside assistance, power outage backup, or industrial power supply, the Door Energy Mobile EV Charger usually has a better chance of generating comprehensive value.

Q2: Can all 420kWh be used for vehicle charging?

A2: The actual output capacity is usually lower than the nominal capacity because the system needs to consider minimum SOC, conversion losses, temperature, and safety reserves. Based on a 10% capacity reserve and 90% overall efficiency, the planned output is approximately 340kWh. Specific figures should be based on project technical documentation.

Q3: Does 420kW mean that each charging gun can output 420kW?

A3: No. The Door Energy device is equipped with four charging guns; 420kW is the total system output power. The control system dynamically allocates power among the four guns based on vehicle demand and charging priority.

Q4: How many vehicles can the device serve at once?

A4: This depends on the amount of electricity each vehicle needs to replenish. Based on a planned available capacity of approximately 340kWh, it can support approximately 34 10kWh replenishments, 17 20kWh replenishments, or 8 40kWh replenishments. The actual number of replenishments will also be affected by vehicle and environmental conditions.

Q5: Can the Door Energy Mobile EV Charger charge large electric trucks?

A5: It can be used to charge large vehicles when the vehicle uses a compatible CCS interface, the voltage is within the 200–1000Vdc range, and communication and current requirements are matched. Due to the large battery capacity of large trucks, projects need to focus on calculating the target replenishment amount, rather than assuming a 0–100% charge.

Q6: How long does the device itself need to recover its power?

A6: Depending on the input conditions, it takes approximately 1 hour using DC charging and approximately 2 hours using a 200kW AC input. The actual charging time will be affected by input power, temperature, SOC, and charging strategy.

Q7: Can the device be used during a power outage?

A7: Yes, provided the energy storage system has sufficient charge stored beforehand. The fleet should set a minimum standby SOC and conduct regular load tests to prevent the equipment from being in a low-charge state during power outages.

Q8: Can it power water pumps, lighting, and electric excavators?

A8: It can be configured based on AC output and load conditions. The device's specifications list a 200kW AC output, but the rated load power, starting current, power factor, interface, and continuous operating time should be checked before actual use.

Q9: Can the device be supplemented with renewable energy?

A9: The device stores electrical energy, and its environmental impact depends on the power source. If the supplemental power comes from solar, wind, or other low-carbon energy sources, the Door Energy Mobile EV Charger can indirectly use renewable energy.