SparkCharge is moving ahead with plans to offer mobile charging as a more-convenient alternative to traditional charging stations.

After testing out its hardware with roadside-assistance services in San Francisco and Los Angeles, SparkCharge on Thursday announced a wider rollout, encompassing an upgraded mobile-charging system called Roadie CCS and a mobile app called ChargeUp.

For a $25 monthly subscription fee, EV drivers in launch markets—Dallas, San Francisco, and Los Angeles—will be able to order DC fast charging wherever their cars are parked. That's more convenient than making a dedicated trip to a charging station, and will also be less expensive than home or public charging, the startup claims (on the home front, perhaps considering expensive wallbox installations).

As the name suggests, the Roadie CCS mobile charger uses the Combined Charging Standard (CCS). We saw some Tesla electric cars in promotional materials, so it seems SparkCharge has an adapter to accommodate them.

SparkCharge mobile-charging service

SparkCharge mobile-charging service

In keeping with standard DC fast-charging practices, the ChargeUp service will only charge cars up to 80% capacity. Charging sessions also have time limits: 50 minutes per session/request for the basic subscription, and 100 minutes for the Premium subscription. Subscribers can make one request per 24 hours, so in a 30-day month that could bring 30 fast charges.

SparkCharge is also pitching mobile charging as a helpful service for EV drivers living in apartments or condos that lack charging stations. Investors (SparkCharge has raised $5 million since its 2017 founding) also seem to see value in mobile charging as a backup plan for drivers, accounting for infrastructure failures or unexpected trips and detours.

What SparkCharge calls a"charging as a service" model fits right in with what the company originally suggested was its goal—a way to use portable hardware to help fill gaps in infrastructure or unforeseen charging needs.

Another potential application for mobile charging, however, might be commercial truck and bus fleets. Last year, Lightning Systems announced a trailer-sized mobile charger, designed to help fleets negotiate around peak/off-peak power use, or provide a boost at locations where DC fast charging hasn't been installed.