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How long can a battery installation charge a bank of EVs?

At Connected Energy, we specialise in using second-life EV batteries to provide power for EV charging hubs. Our installations essentially provide a power boost to sites with limited capacity – extra power for times of peak demand.


Many organisations are looking to electrify their own fleets, however, lack the available power capacity to charge many vehicles at once, especially at peak times. Battery storage can help mitigate some of this demand avoiding often costly new grid connections.

One question we get asked a lot is, how long can a battery installation like our E-STOR system charge EVs?

The short answer is that it depends – there’s a range of variables that need to be taken into consideration. However, battery energy storage is not a theoretical idea, our E-STOR system is a fully commercialised product. So, we can provide some real-life examples of how E-STOR works for EV charging hubs.

Example: a public charging hub

At Dundee in Scotland, we are providing two E-STOR 300/360 systems for the City Council’s charging hubs – one public and one private. The 300/360 stands for up to 360kWh of power stored in our E-STOR system and delivered at a rate of up to 300kW.

The innovative charging hubs combines solar PV arrays with our systems and a range of fast, rapid and ultra-rapid chargers.

On the side accessible to the public, it combines our E-STOR 300/360 with 22, 7kW chargers, two 50kW chargers and a 100kW charge point. E-STOR’s batteries are replenished by the solar array and it can also recharge from the grid if required.

With 25 chargers of varying sizes on site, the answer to “how long can E-STOR operate the chargers?” can significantly vary, too. Here are a few scenarios:

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1. Fast chargers

With 22 public fast chargers on site, each 7kW, this equates to total power demands of 154kW if they were all in use at the same time. In ideal conditions, E-STOR could power all these fast chargers continuously for around 2 hours before the batteries needed to be recharged.

2. Rapid and ultra-rapid chargers

There are two 50kW rapid chargers on site, equating to total power demands of 100kW. Our E-STOR system could power both chargers, continuously, for over three hours. The same figures apply if E-STOR was running the 100kW charge point on its own, or it could run all three continuously for almost two hours.

3. Mixed use

A more likely scenario is demand spread across the different available chargers, for example running seven of the 7kW charge points and one of the 50kW chargers concurrently. In this scenario, E-STOR could power all eight charge points continuously for almost four hours.

Of course, the demands on the charging hub will peak and trough depending on how many vehicles are plugged in at once and what type of charger they use. Taking the example of a Tesla, you can fully recharge it in about two hours on a 50kW rapid, but it is more likely to be there for a top-up charge, meaning a much shorter charging time. E-STOR can recharge its batteries from the grid and the solar array, meaning it can replenish the stored energy when not in use.

Example: Allego

Allego is a leading provider of EV charging infrastructure. The Dutch company is building an international charging network with more than 28,000 charge points operational throughout Europe.

Allego installed 50kW rapid chargers on the motorway near the German town of Kirchheim. However, the local grid connection could only support 40kW. Allego had to either invest in an expensive grid capacity upgrade, or a much more cost-effective energy storage system.

We supplied Allego with our E-STOR 60/90 system, which provides 60kW of power. Thanks to our active load management technology, the chargers can only provide 50kW when there is sufficient power available from the grid and E-STOR combined.

The system we installed is designed to provide the additional 10kW that the site needs each time a car is plugged in. It has the capacity to provide this extra buffer for a continuous charge of six hours.

Systems the size of Allego’s are therefore designed for occasional use by EV drivers – plus, the grid can refill the batteries whenever there are no EVs plugged in for a charge. Read more about our work for Allego.

Ask the experts

Connected Energy is one of only a handful of companies in the world so far to have successfully deployed second life batteries in real-world applications. We have proven products for EV charging hubs that are designed to meet the needs of fleet, workplace and charging hubs. Download our recent EV charging guide to discover more about how battery energy storage can support EV charging.

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Get in touch with our team to discuss whether battery energy storage can work for your business.