Extending The Life Of EV Batteries

April 26th, 2023

Comments Feed

One of the big questions that a lot of people have about making the shift from ICE (internal combustion engine) vehicles to EVs of any sort is the issue of battery life.  In this context, battery life doesn’t refer to how many kilometres the batteries will take you (this is technically known as battery range) but the actual lifespan of the battery unit itself.  If you’ve had any experience with any kind of rechargeable battery – which most of us have had – then you’ll know that even though you can recharge a battery a certain number of times, you can’t do it forever and eventually the battery will die, never to be recharged again.

Having said that, the lifespan of EV batteries is pretty good. In fact, the manufacturers claim that batteries can last for about 10–12 years, which is longer than the average lifespan of a whole car in some countries (although those who like second-hand cars or who are into classic cars may raise an eyebrow at this statistic). They’ve also got warranties to ensure that they last for a certain amount of time.

However, people researching rechargeable batteries don’t tend to measure the lifespan of batteries in terms of time (partly because no scientist in a rapidly developing field wants to spend 10 years running an experiment). Instead, they measure the lifespan of a rechargeable battery in charge–discharge cycles. To understand why they do this, we need to understand a bit about the science of a rechargeable battery.  Don’t panic – I won’t get into too much detail, partly because I don’t have a PhD in it and can’t wrap my head fully around some of the minute details.

In any battery, an electrical current is generated when ions (particle with an electrical charge) move from the negatively charged anode through an electrolyte to the positively charged cathode. This keeps going until everything balances out and the electrochemical reaction stops.  You can do this yourself with a copper coin (if you can find one these days), a zinc-coated nail and a lemon. Attach a wire to the coin and the nail, maybe connecting fairy lights in the middle, stick them in a lemon and watch the lights glow. However, in a rechargeable battery, this processed can be reversed, shuttling those ions back to the anode again.

In a rechargeable battery, every time the reaction comes to an end, i.e., complete discharge, that’s considered to be a full cycle.  In the lab, to test a battery’s lifespan, researchers charge and drain and charge and drain and… until the material in the anode and/or cathode starts to deteriorate, which all things do over time.  They also measure capacity decay. Over time, any rechargeable battery will lose the amount of charge it can store. Again, this is related to the number of charge–discharge cycles.

So what does that mean for EV batteries?  Although the manufacturers measure lifespan in years, this figure is based the ideal battery user.  If you charge your battery the right way and use it in the right way, then you’ll get the maximum lifespan from your EV’s battery pack. However, if you don’t, you’ll shorten the lifespan of the battery.

You can imagine the number of charge–discharge cycles in a battery as kind of like lives in a computer game.  You’ve got a lot of them, but every time, you get those hit points down to zero and have to “respawn”, you’ve used up another life.  However, unlike a computer game character’s life, hitting either extreme (full charge as well as full discharge) will shorten the lifespan because it puts stress on the battery – kind of like keeping a bow fully strung and at full draw most of the time, which, as any archer will tell you, isn’t good for the bow.

This means that ideally, you should avoid hitting these extremes.  This means that exhausting your battery’s charge completely is a bad idea.  However, so is topping it up to 100% all the time.

At this point, those of you who are familiar with rechargeable NiCad batteries will be scratching your heads because you’ve heard of “battery memory”.  NiCad rechargeables (these are the sort that you buy to put in things that come with the label Batteries Not Included) do have a “memory”, meaning that if you are in the habit of recharging the batteries when they hit 10% charge, they’ll start acting as though 10% is the new zero.  However, lithium ion batteries don’t have a battery memory effect, meaning that you won’t reduce their charging capacity if you top up the battery’s charge when it dips below a certain level.

In fact, what manufacturers recommend for preserving the life of a battery sounds rather like the principles used for managing blood sugar in Type 1 (insulin-dependent) diabetes.  You don’t want things to drop too low, but you don’t want them to go too high, either.  The ideal is to keep batteries between 80% charge (which is why the charging times given by EV manufacturers are usually the time taken to reach 80% charge) and either 20% or 40% charge. On top of that, rapid charges and rapid discharges also stress the battery.

In practice, this means the following:

• Don’t recharge your EV to overnight every night. However, you need to balance this against what you know about how and where you’ll be driving and where the accessible chargers are.
• Don’t let the battery drain too quickly. This means that you have to be very careful when it comes to things like towing, going uphill and running too many things that require electricity at once.  In other words, if it’s a freezing cold rainy night when having the lights, wipers and heaters going is a must, then you have to decide if it’s really worth it to use the sound system as well.
• Although DC rapid charging is convenient, it does stress the battery, so reserve this for when you absolutely have to.  DC rapid charging isn’t catastrophic for your EV’s battery and you can do it now and then without putting a serious dent in your lifespan, but it does put a bit more stress on it than slower AC charging, so don’t do it all the time.
• Extreme temperatures make the lithium in the batteries do funny things.  Getting too hot is the most dramatic, but most modern battery packs (thank goodness!) have cooling systems to ensure that they don’t overheat (these systems use the battery’s own charge to operate).  Getting too cold is also a problem, as the electrochemical reaction producing the charge is slowed right down, which translates to reduced range and slower charging times. Some battery packs, notably in Tesla vehicles, have systems that keep them at the ideal temperature – though at the cost of range. However, these can drain the battery more quickly, which shortens the lifespan.
• If your EV has to go into long-term storage, keep it on a trickle charger or a smart charger to ensure that it stays about half charged.