by Larry Magid
This post first appeared in the Mercury News
Based on what I’ve seen on forums, there is a lot of confusion about EV battery maintenance along with plenty of “range anxiety.” Here are some basic facts about EV batteries that might help reassure you and extend the life of your EV battery.
Battery chemistry matters
In almost all cases, the batteries are Lithium-Ion (Li-ion), but there are different chemical configurations that impact how they operate and how you manage them.
Most of the EVs currently on the road are equipped with nickel, manganese, and cobalt (NMC) batteries, but an increasing number now come with a lithium iron phosphate (LFP) battery. Newer Standard Range Tesla Model 3s, for example, use LFP, while the long-range use NMC, because NMC has greater density, which provides about 30% more energy from the same size battery. But LFP batteries have some advantages, including lower cost and longer life, because they can be charged more often with slower degradation than NMC. They are also less likely to cause a fire, though EV vehicle fires are extremely rare, especially compared with gasoline cars. LFP batteries are also said to be more environmentally responsible, because the materials they use are more abundant, safer to mine and safer to dispose of or recycle. And, unlike NMC batteries, they can be safely charged to 100% on a daily basis.
Tesla and some other EV carmakers recommend you charge cars with an NMC battery to 80% for daily driving, although Tesla recommends charging cars with LFP batteries to 100% at least once a week. It’s OK to charge any battery to 100% if you’re about to leave on a road trip, but don’t make it a regular habit and don’t leave it at 100% for a prolonged period because that can have a detrimental impact on battery health.
EPA estimates are not real-world
EPA range estimates are theoretical and not real world. The vast majority of drivers will get less than the estimated range. Just as with gasoline cars, how much depends on many factors, including speed, temperature (EVs are less efficient in cold weather), weight of passengers and luggage and terrain. In 2023, Consumer Reports did a real-world range test on several luxury EVs, and of the 22 EVs tested, nearly half fell short of their EPA-estimated range.
“When driven at a constant highway speed of 70 mph, some vehicles we tested fell up to 50 miles short of their advertised ranges, while others exceeded their advertised ranges—one by more than 70 miles,” Consumer Reports said.
If you’re in the market for a new car, LFP is probably a better (and less expensive) option if you plan to use your car mostly for local driving. For example, you can easily make a round trip to anywhere in the San Francisco Bay Area on just about any late-model EV. But if you like to take road trips, especially to places where you might have trouble finding a charging station, a long-range vehicle gives you greater peace of mind.
I drove a Model 3 with an estimated 264-mile range (actual range after 5 years was closer to 200 miles) and never ran out of juice on several long road trips, but there were a couple of stressful situations where I worried. I eventually replaced it with one with a a long-range EPA rated at 341 miles, mostly to reduce my stress levels on long trips.
The 80-20 charging rule
With the exception of cars with LFP batteries that can safely be charged to 100%, the general “80-20 rule” is to charge to no more than 80% on a daily basis and keep the car charged to at least 20% on a regular basis. Again, that doesn’t mean all the time. It’s fine to charge to 100% right before a road trip, so long as you burn off some of those miles relatively soon. I haven’t been able to determine exactly how long it’s safe to leave a car at 100%, but my strategy is to charge my car to between 70% and 80% on a daily basis. I generally charge to about 90% to 95% just before I leave on a long trip. If I’m at a charger and know it will be a long time before the next one, I might charge to 100%. However, the fuller your battery, the longer it takes to charge. Getting a car from 80% to 100% might take as long as getting from 20% to 80%, so if I know there are chargers within range, I’ll generally stop at 80%, unless I’m enjoying lunch and want that extra time to fill my belly as well as my car’s battery.
It’s fine to arrive at your destination with less than 20%. When you plan a long trip on a Tesla, the navigation system recommends charging spots that typically estimate your battery on arrival as low as 10%, and they often recommend very short charging stops because you’ll spend less time charging if you keep the levels low even though it might mean more stops. But I’m more conservative, because I want to be safe in case there is a long detour or some other unforeseen event. For example, I was once driving from Los Angeles to the Bay Area and had to take a windy road over the mountains because Pacheco Pass, the usual route, was closed. Had I followed Tesla’s recommendation, I would have likely run out of power before reaching a Supercharger.
Getting there and back
Another thing to consider is getting from your destination to another charger. Tesla, for example, will navigate you to a destination with enough of a charge to get there but not necessary enough to get to another charger on the way home or your next destination. If your EV supports entering more than one stop, enter both your destination and either the location of a known charger or your home or next stop to see whether you can get a charge to continue your trip. If it doesn’t try plotting the trip using the A Better Route Planner app. It’s not uncommon for non-Tesla charging stations to be out of service so try to verify it’s working if you can. You may be able to find a hotel with a destination charger and, if so, give them a call to see if the charger is working and available to use.
Storing the EV in hot weather
If you’re parking your car for an extended period of time in what could be very hot weather, such as when you’re going to be away on a trip during the summer, it’s a good idea to reduce the charge level to about 50% or lower to avoid degradation from the heat.
Don’t trust the range estimator
EVs have range estimators similar to gas gauges on cars. In most cases, they will estimate both the percentage of remaining battery and the estimated number of miles left before you run out. These are good general guidelines, but you should not rely on them, especially the estimated remaining miles, which doesn’t necessarily account for terrain, your speed, temperature and other important factors. Teslas have a battery app that gives you a more accurate estimate, but even it’s not perfect. I just give myself some margin.
Relax, it’s going to be OK
Range anxiety is a common occurrence for EV drivers, but, especially if you have access to Tesla’s Supercharging network, it’s mostly misplaced. With some planning, you should be able to get almost anywhere on major highways, although you may need to do some extra planning if you go off the beaten path. If you do go to remote areas, consider finding hotels with overnight charging, which is often included in the room price. Use the app and website called A Better Route Planner, which does an amazing job helping you plan charging stops. I’ve driven more than 50,000 miles in an EV to all sorts of places, and despite some range anxiety, my EV has always gotten me there and back. Tesla is opening its extensive charging network to other EVs, so if you’re in the market for an EV, I highly recommend you pick one that will be able to charge at Tesla Superchargers. If you currently have a non-Tesla EV, check to see if there’s an adapter you can get for the Tesla network.
And try not to worry even if you occasionally fail to heed this advice. Modern EVs are equipped with battery management systems that do their best to mitigate battery degradation, regardless of what type of battery you have. If you’re looking for reassurance, search for “8 lessons about EV battery health from 6,300 electric cars” for some statistics about EV batteries.