Lithium-ion batteries used in modern solar systems and electric vehicles (EVs) can last over 15 years and still have plenty of use after consuming their rated life cycles, as long as they are treated according to their specifications.
South Africans on social media often respond sceptically to announcements of new EVs, asking what new buyers would do if the battery packs up within a few years.
Part of this misconception about battery life might be down to people’s experience with low-voltage lead-acid batteries used to help start a vehicle and sustain lights or entertainment systems over a short period.
These batteries typically only last 3 to 5 years before requiring replacement.
When used for home backup, their lifetimes can be shortened substantially because they are not intended for deep discharges.
Most lead-acid batteries should not be discharged below 50% of their capacity.
However, the lithium-ion batteries powering most EVs and modern home backup systems are designed to be discharged significantly more with less degradation to their overall lifespan.
One of the common metrics used to indicate how long a battery should last is its cycle life.
Modern lithium-ion batteries are typically rated to last for over 3,000 cycles, compared to the 200-300 cycles of lead-acid batteries.
What is essential to understand about electric vehicle battery lifespans is how long a lithium-ion battery can last and what happens after its cycles run out.
The first point to clarify is that there is a distinction between the depth-of-discharge (DoD) rate and a cycle.
The depth-of-discharge (DoD) refers to the extent to which a battery can be safely drained without causing strain that might result in excessive and premature losses in capacity.
The most common DoD for lithium-ion batteries is 80%, so these can be safely discharged to 20% of their total capacity.
Certain batteries also have 90% or even 100% DoD ratings, like the Tesla Powerwall 2.
Another point of confusion is how the depth of discharge differs from what is considered a full charge-discharge cycle.
ScienceDirect defines cycle life as the number of cycles with a 100% DoD that a cell can perform before its capacity drops to 80% of its initial specified capacity.
Reputed battery companies will always consider a cycle to be a complete 100% discharging and recharging course.
If you use only 50% of your battery’s capacity daily, a cycle will only be consumed after two days of use.
However, exceeding the maximum DoD can lower the total number of cycles.
This is one of the factors that shortens smartphone batteries’ useable lifetimes, because users often deplete these to well below 20% or even 10%.
With these factors taken into account, one can take a realistic look at how long a home backup or EV battery will last.
Home backup batteries can be rated for well over 5,000 life cycles. For example, the Dyness 5.12kWh DL5.0 battery has 6,000 cycles.
Even if you deplete this battery’s capacity daily — while keeping within the 90% DoD rate and not exceeding the battery’s C rating — it should last for 16 to 17 years before hitting 80% of its original capacity.
From that point, the battery will still be very useable, but capacity losses will accelerate.
Reputable backup battery manufacturers generally offer a warranty for free replacement or repair if the battery’s capacity drops below 80% within ten years.
Modern EV batteries typically have at least 1,000 cycles before dropping to 80% capacity, in worst-case scenarios.
The most affordable EV in South Africa — the GWM Ora 03 — consumes 16kWh per 100 kilometres and has a useable capacity of 45.5kWh.
Therefore, it should be able to drive around 284km on one cycle.
According to Numbeo, the average South African commuter travels about 44km per day.
Over an entire year, that would work out to 16,060km, less than 57 full cycles.
At that rate, it would take between 17 and 18 years for the GWM Ora 03’s battery to reach 80% of its original capacity, based on an estimated cycle life of 1,500.
One real-world example of the slow capacity loss of an EV battery is the 2016 BMW i3 owned by South African Shaun Maidment.
It clocked over 300,000km in five and a half years and retained roughly 85% of its original capacity.
Making this even more impressive is that the BMW i3 is from the first wave of mass-produced EVs. Since its launch, EV battery tech has improved substantially.
Major EV manufacturers are so confident of the reliability of batteries that they offer extensive warranties on them — typically guaranteeing 80% of the original capacity for eight years or 150,000km, whichever comes first.
Another factor to consider is that EV battery prices are expected to reduce substantially as the greater adoption of EVs boosts economies of scale.
By the time the battery on an electric car bought today needs to be replaced, prices will be substantially cheaper. In addition, recycling processes for lithium-ion batteries should be well advanced. Between 80% and 90% of EV battery components are recyclable.
In fact, many of the batteries used for home backup come from stripped EVs in China, with their rated capacities adjusted to compensate for the losses they experienced while in use.
Therefore, you should be able to trade in your old battery and might get a discount on a new one if you plan to keep using the same car.
