EV charging best practices: How can you keep your battery healthy?

The battery pack is the most expensive part in any EV, so keeping the battery healthy is the best way to get the full value out of your investment—not to mention the best way to keep yourself on the road for longer between charges.

If you’ve experienced battery degradation with a phone or laptop, you might be worried that the lithium-ion battery in your car may similarly lose capacity over time and leave you increasingly tethered to a charger. While all lithium-ion batteries will lose some capacity over time, the good news is that battery technology keeps improving, and the durable lithium-ion batteries installed in electric vehicles have been designed to retain much of their charge capacity as they age (on average, losing around 2.3% per year). 

 The latest research suggests that if you follow these guidelines (and any other recommended by your EV manufacturer), you’ll optimize your EV battery’s health and protect it for the long haul.

Regularly charging your battery above 80% capacity will eventually decrease your battery’s range. A battery produces electricity through chemical reactions, but when it’s almost fully charged, all the stored potential energy can trigger secondary, unintentional chemical reactions. These reactions aren’t dangerous, but over time they’ll reduce the efficiency and capacity of your battery.

 Similarly, charging your battery before you dip too much below 20% isn’t just about peace of mind; it can also contribute to better battery health. Lithium-ion batteries perform less efficiently at low states of charge, and they perform better over the long term when they are only partially re-charged each cycle. So going from a 20 to an 80% charge is kinder on your battery than going from 0-100%. 

 The 20-80% rule is especially important if you don’t drive your EV regularly or plan to store it for a long period of time. If this is the case, Qmerit recommends charging the battery to 80% at least once every three months to protect against damage that may result from a completely depleted battery.

Battery scientists generally recommend Level 1 or 2 over Level 3 fast charging because fast charging’s higher current rates generate additional heat, which is tough on batteries. 

In real-world tests, however, fast charging doesn’t seem to have a significant impact on battery capacity. The Idaho National Laboratory concluded that the difference in capacity loss between 2012 Nissan Leafs charged at Level 3 versus Level 2 was “small relative to total capacity loss.”

According to Liz Najman, Director of Market Insights at Recurrent, “there is a difference between what has been observed in laboratory scenarios and what will actually happen in EV batteries, which have many cells, along with thermal and voltage protection and management systems.”  

In newer model EVs with sophisticated battery management systems, frequent fast charging may not cause any additional battery degradation. Recurrent found “no statistically significant difference in range degradation” between Teslas that almost always used DC fast chargers and those that almost never did.

Level 1 or 2 charging still has its advantages, as it’s likely cheaper and more convenient for drivers who can plug in at home overnight. By all means, though, use fast chargers when expedient. Just be sure to follow the manufacturer’s recommendations for preconditioning the battery.

Driving and charging in extreme temperatures can reduce range and put additional wear and tear on batteries, and the higher currents used in DC fast charging can exacerbate the stress on the battery from those extreme temperatures. That’s why EV battery management systems limit the charging speed to protect batteries when they are too hot or too cold.  This is good news for battery health, but bad news for drivers in a hurry and paying by the minute.

Can you still take advantage of Level 3 charging on very hot or cold days?  Yes, but it requires a little bit of advanced planning and depends on your particular make and model.  Most newer EVs will automatically bring the battery to the ideal charging temperature once you’ve set a DC fast charger as a destination in the navigation system.  Just make sure to do so at least 20-30 minutes before you plan to plug in to give the battery time to condition.  

If you drive an EV without a preconditioning feature, you can still take some steps to prepare your battery.  Najman recommends “driving the car a bit before fast charging in cold weather, and letting the battery cool down before fast charging in the heat.”