HUB 05 · The Charge Curve
Battery Preconditioning for Fast Charging
The reason two identical EVs can charge at wildly different speeds - and the button that fixes it.
We earn a commission when you buy through our Amazon links, at no extra cost to you. It never affects our rankings, and we say so when the cheaper product is the better buy. How this works.
Two drivers pull into the same fast charger in the same car. One charges twice as fast as the other. The difference is usually not the charger - it is battery temperature. A cold pack charges slowly, and preconditioning is how you fix it: warming the battery to its ideal window before you plug in so it accepts full power from the first minute.
Why cold batteries charge slowly
Lithium-ion cells have a preferred temperature range for fast charging - roughly warm, not cold. When the pack is cold, the chemistry slows, and pushing high power into a cold cell risks damage (lithium plating), so the car's software throttles the charge rate to protect it. That is why a winter fast charge, or a charge right after a short drive from a cold garage, can crawl at a fraction of the car's rated speed - the pack simply is not warm enough to safely take more. It bends the whole charge curve downward.
What preconditioning does
Preconditioning uses the car's thermal system to warm the battery to its fast-charge window before you arrive, so it is ready to accept full power the moment you plug in. Done right, it can be the difference between a 20-minute stop and a 40-minute one on a cold day. It costs a little energy to heat the pack, but you make it back in charging time and a gentler session.
How to trigger it
- Navigate to a fast charger.On most modern EVs, setting a DC fast charger as your destination in the car's own navigation automatically starts preconditioning so the pack is warm on arrival. This is the easiest method and the one to rely on.
- Use a manual precondition button.Some cars offer a manual "precondition battery" or "charge prep" control in the menus for when you are not using the built-in nav.
- Time it. Preconditioning takes a while to warm a cold pack, so trigger it 20-45 minutes before you plug in - which is exactly what routing to the charger handles for you.
Preconditioning is a fast-charging tool, not a home-charging one. On home Level 2, power is low enough that a cold pack is not a problem - you plug in overnight and let it charge gently. Save preconditioning for cold-day road trips.
The takeaway: if your fast charging feels slow in winter, the battery is probably cold. Route to the charger in the car's nav, let it warm the pack, and you will hold the fast part of the curve far longer.
Questions
Frequently asked
What is battery preconditioning?
It is the car warming its battery to the ideal temperature for fast charging before you arrive, so the pack accepts full power immediately instead of charging slowly while it heats up. Most EVs start it automatically when you navigate to a DC fast charger.
Why does my EV fast-charge so slowly in winter?
A cold battery cannot safely accept high power, so the car throttles the charge rate to protect it. Preconditioning - warming the pack before you plug in, usually by routing to the charger in the car's navigation - restores full charging speed.
Do I need to precondition for home charging?
No. Home Level 2 charging delivers low enough power that a cold battery handles it fine, so there is nothing to precondition. It only matters for DC fast charging, where a warm pack charges much faster.
Keep reading
Related
Receipts
Sources
We do not run a testing lab, and we do not pretend to. Where a measured number came from someone else's lab, we name them and link them. Where we could not verify something, we say so on the page rather than quietly leaving it out. Read our full method.