Here’s a quick guide to charging speeds for your EV
When charging your EV, you’ll see the charging speed (or power, shown in kW) rise and fall depending on a few different factors.
The golden rules to faster charging are:
1. EV or charger limits
First of all, there are the two factors which won’t change:
🚗 The maximum speed your EV can accept
🔌 The maximum speed the charger can supply
This means that even if the charger can happily dish-out 150kW, but your EV has a maximum charging speed of 50kW, you’re never going to see anything more than 50kW, as that’s all your EV is built to accept. Similarly, if your super-duper EV can accept 200kW, but you’re at a charger with a maximum power of 50kW, that’s the highest you’ll see as that’s all the charger is designed to supply.
2. EV throttling
However, there are then a couple of variables which could limit your charging speed even when the charger and your EV are capable of more. This is typically indicated on the charger with the text ‘vehicle limits’ to show what’s limiting charging speed.
📉 State of charge (or battery percentage)
As your EV’s battery fills up, it will be able to accept less and less speed. This is to do with the battery’s chemistry, meaning you’ll see the highest speeds typically low in the battery (around 10%), then speeds will drop as the battery fills up, usually dropping off significantly over 80% or 90%.
This isn’t anything wrong with your EV the charger, it’s simply your EV telling the charger to slow down as it fills up to protect the battery. This maximum allowable speed depends on each and every EV, and follows what’s called a ‘charging curve’ – you can find your EV’s on the EV Database.
📚 Top tip: It's often quicker to do two short charges between 0-50% than it is to do one long charge 0-100%. If you're looking to minimise your time spent charging on a trip, charge whilst your battery is emptier, and check your EV's charge curve for the quickest area to charge is (you can do this on the EV Database).
🔋 Battery Temperature
Your EV is quite temperature sensitive, and will change the maximum allowable charging speed depending on its battery temperature. So, the charging curve you’ll see for your EV is what to expect at around 25ºC, but anything lower and the speeds the battery can accept will drop.
You can warm up your EV’s battery by pre-heating/pre-conditioning on the way to the charger, so by the time you’re there it’s already nice and toasty. You can find how to do this in your EV’s settings/navigation system (though this isn’t available on all EVs).
Rapid and ultra-rapid charging also warms up an EV’s battery because of the high-power going into it. This means you may see low speeds for the start of the charge whilst your EV’s battery is warming up, then it will be able to accept higher speeds as it reaches its optimum temperature.
📚 Top tip: Even if you think it's not too cold outside, your EV's battery may have been out in the cold for a while, and it needs to be ~25ºC all the way through to be ready to reach the highest speeds. Pre-heat your EV's battery on the way to a charger, or accelerate/regenerate a few times before you charge to get some heat into the system!
3. Charger throttling
This is less common, but the charger may limit your charging speed too.
🚗 Power sharing
This can happen if you’re at a charger which shares power with adjacent EVs or across a Charging Hub, so if you can it’s best to leave gaps where possible.
📚 Top tip: Most of our Charging Hubs feature Kempower ultra-rapid chargers. These are pretty clever, so will share charging power across a whole Charging Hub instead of splitting power between adjacent bays. This means power sharing rarely occurs, especially at larger Charging Hubs.
⚡️ Voltage mismatch
Some chargers only support charging up to 500V, which means if you're charging a vehicle on 800V+ system architecture, it will be limited by its maximum speed in 500V mode.
📚 Top tip: The charger's maximum reachable voltage and amperage can be seen in the 'i' menu on the charging screen. You can find your EV's maximum charging speed, system voltage and charging curve on the EV Database.
📈 Boost mode
Some chargers also ‘boost’ their speeds, where you may see maximum speed for a certain period of time or until a maximum pin-temperature is reached, after which it may fall to slower speeds. This is usually indicated on the charger with the text ‘charger limits’ or ‘grid limits’.
📚 Top tip: Think the connector your charging on has reached the end of its boost phase? Try another connector that isn't in use, as that will be able to support another boost!
When you plug in and pay for your charge, your EV and the charger do what’s called a ‘handshake’, where they talk to each other to figure all the complicated stuff out. Then, your EV will decide on the amount of power it can accept at that time, and request it from the charger.
So remember, it's the EV that sets the charge speed, the charger is only doing as your EV asks!