Free
Battery-buffered EV charging calculator
This free battery-buffered EV charging calculator estimates the battery size and output you need to run fast chargers on a limited grid connection, and how long it takes to refill.
Calculator
Size your battery-buffered charging
Your results
Estimates to guide planning, not a design.
–kWh usable battery energy
–kW battery output
–minutes per charging session
–hours to refill the battery
–kW connection needed without a battery
–kW per vehicle without a battery, all points busy
Assumptions and disclaimer. Results are planning estimates, not a design. Each session charges at the lower of the charger power and the vehicle's acceptance; real DC charging slows as the battery fills, so sessions take longer and peak power is reached only for part of each session. Battery output covers the gap when every point charges at full power at once. Battery energy covers the busy-period energy the grid cannot supply, plus 25% for conversion losses, ageing and a reserve. Refill time assumes the full grid allowance is free to recharge the battery during quiet time. Check results with half-hourly site data, vehicle specifications and supplier modelling.
How to use it
Getting reliable results
Get the inputs right
Use the grid power left after the site's other load
Size for the busiest hour, not an average day
Use the energy your vehicles really take per session
Check each vehicle's maximum DC charging power
Reading the results
Battery output fills the gap when every point is busy
Battery energy covers what the grid cannot in the busy period
Refill time must fit before the next busy period
Amber messages show where to look harder
Questions
Frequently asked questions
What is battery-buffered EV charging?
Fast chargers paired with a battery that fills from a modest grid connection and boosts output when vehicles charge, so a site can offer fast charging without a large upgrade.
How big a battery does battery-buffered EV charging need?
Enough usable energy to cover what the grid cannot supply during the busy period, plus a margin, and enough output to fill the gap when every point charges at once.
How long does the battery take to refill?
Roughly its usable energy divided by the grid power free to recharge it. It needs to refill before the next busy period.
When is a battery better than a grid upgrade?
When an upgrade is slow or expensive, demand comes in peaks with quiet periods in between, and the battery can also cut peak-time electricity costs.
Why does vehicle charge acceptance matter?
A vehicle charges no faster than its own limit, so chargers or batteries sized above it add cost without saving time.
Is the result a design?
No. It is a planning estimate. A full design needs half-hourly site data, vehicle specifications and supplier modelling.
Further reading
Battery-buffered charging insights
Insight
When does battery-integrated fast charging make sense?
The sites where storage beats an upgrade.
Learn more
Insight
Why battery-boosted EV charging matters
Fast charging from a modest connection.
Learn more
Insight
Battery-buffered charging vs a grid upgrade
Comparing the costs over ten years.
Learn more
Insight
Battery storage for grid constraints
The questions to ask first.
Learn more
Talk to us about battery-buffered charging
Send us your results and we will tell you plainly whether storage, a grid upgrade or a mix makes most sense for your site.