Most new EV owners hear about the 80% rule in their first week, then spend a month wondering if they are wrecking the battery. You are not. Here is how The Conduction Company explains the rule to clients when we install a home charger in Auckland.
The short answer. The 80% rule means charging your EV to about 80% for everyday driving, rather than to full. The Conduction Company's advice, from installing home chargers across Auckland, is to keep a nickel-based battery between 20% and 80% day to day and charge to 100% only before a long trip. LFP batteries are the exception: keep those at 100%.
What does the 80% rule actually mean?
Charge to about 80% of the battery's capacity, then stop, for normal use. The point is battery lifespan. EVs run on lithium-ion batteries, in two main families. Nickel-based packs (NMC or NCA) are in the Hyundai, Kia, Nissan Leaf, and Tesla Long Range and Performance models. Lithium iron phosphate (LFP) packs are in every BYD, the MG4 Standard Range, and the rear-wheel-drive Tesla Model 3 and Model Y sold here. The 80% rule is for the nickel-based family. Those batteries have an optimal band, between about 20% and 80% state of charge, and that is the band The Conduction Company tells clients to live in. LFP is a different story, covered in the next section.
Your phone does the same thing. iPhone 15 and later let you cap charging at 80% for exactly this reason, and even then the phone tops up to 100% now and then to keep its gauge honest. Sitting at 100% every day is what wears a nickel-based battery faster. Running it flat does harm too. Stay inside the 20% to 80% band for daily use and the battery lasts longer. That is The Conduction Company's standing advice for a nickel-based pack.
What happens when the dash says 0%?
The car shuts itself down a little before the cells are truly empty, so a displayed 0% is the car protecting itself, not spare range you can use. Tesla's manual says not to assume any range is left at 0%, and Nissan, Hyundai, and BYD all say the same thing next in theirs: plug in straight away, because a car left sitting flat can damage the battery, and that damage is not covered by warranty. The Conduction Company's advice is to treat 20% as the floor. The buffer is a safety net, not a plan.
Does the 80% rule apply to LFP batteries?
No. If your car has an LFP battery, the maker's advice is the reverse of the 80% rule: set the charge limit to 100% and charge to full at least once a week. Tesla's manual says to keep an LFP car at a 100% limit even for daily use, and to fully charge it at least once a week. BYD's Atto 3 manual for New Zealand says the same, a full charge at least once a week. MG tells MG4 owners to carry out a full slow charge at regular intervals, and the car reminds you if you do not. The reason, as The Conduction Company explains it to clients, is the gauge. An LFP battery's voltage barely changes between 20% and 90%, so the car's range estimate drifts unless it sees 100% now and then.
Not sure which you have? Your manual or the charging screen tells you. On a Tesla, a slider marked "50%/100%" means LFP and "Daily/Trip" means nickel. The Conduction Company's short version for Auckland clients: nickel-based pack, live between 20% and 80%. LFP pack, charge to 100% and do it weekly.
Should I charge my EV to 80% every night?
Yes, for ordinary driving in a nickel-based car. Most newer EVs let you set a charge limit, so set it to 80% and leave it there. Plug in when you get home and the car stops itself overnight. The Nissan Leaf, the most common EV in New Zealand, has no charge limit setting. Leaf owners use the charging timer, or a wall charger that can stop at a set time or a set amount. Either way, The Conduction Company's advice is to set it once and forget it. The car or the charger does the work, and you never think about the rule again.
Should I charge my EV to 100% every night?
Not in a nickel-based car, but charging to 100% once in a while is fine. If you are driving down the North Island tomorrow, set the limit to 100% tonight and take the full range. A one-off full charge does no measurable harm. Time it to finish close to when you leave rather than days before, because it is sitting full that ages the cells. The 80% rule is a daily habit, not a hard limit. Jordan Statham, director of The Conduction Company and a registered electrician and electrical inspector, puts it this way:
"It's fine once in a while to top it right up to a hundred ... it's not really going to harm it if it's just a one-off. It's just a general rule that it's nicer for the battery to stay between 20 to 80 percent in daily use." Jordan Statham, The Conduction Company.
What about range anxiety?
Range anxiety is real, and it hits brand new EV owners hardest. Anyone who has owned one knows the feeling of watching the number drop and wondering whether you will make it home or to a charger. Running out before you get there is a real problem, and nobody wants to do it twice.
It passes. In The Conduction Company's experience, most owners know their car's real range after about six months of driving it, and they know where the 20% to 80% band gets them in a normal week. The rule stops feeling like a limit once you know your car.
Does Auckland's climate change the advice?
Only a little. Cold does two things. A cold battery cannot give up all of its energy until it warms, so the range figure reads lower on a winter morning, and the cabin heater draws from the same battery. The energy is not lost, just parked until the pack warms up, and the heater is the bigger cost. Recurrent's study of more than 30,000 EVs found the average car keeps about 78% of its range at freezing point. Auckland rarely gets there, so The Conduction Company tells clients to expect a smaller winter dip, mostly from the heater. That is normal, and it is not a fault.
Most newer EVs heat and cool their own battery to keep it at a stable working temperature. The Nissan Leaf does not, which is one reason its battery health varies so much between cars. In colder countries some cars preheat the battery before a morning departure, because the coldest winter days can cut performance hard. Here, The Conduction Company's advice is simply to expect a shorter winter range and plan around it.
Why do public fast chargers stop at 80%?
This is the other 80% rule, and it is about queues, not battery life. A DC fast charger slows right down once the battery passes about 80%, on every EV, by design. ChargeNet sets 80% as its default for that reason, and will not let you go past 95%, because the last few percent can take as long as the first 95% for a few kilometres of range. EECA and NZTA say the same: take what you need, and unplug at 80% if someone is waiting. A home wall charger does not taper like this, so The Conduction Company's advice for home charging is unchanged. Your limit is set by the battery type, not the charger.
What charger does The Conduction Company recommend for an Auckland home?
A faster one. When a client is worried about range, the best fix is a 32 amp wall charger, and that is what The Conduction Company fits on most home EV charger installations in Auckland . It is the best of all worlds. You can turn the current down and trickle charge overnight if you prefer. You can set it to charge for a set number of hours, or only when your power plan is on a cheaper rate. And when you need the full amount, it delivers.
The figure that settles most clients: on a 32 amp charger, The Conduction Company sees a car go from 10% to 90% in about five hours, and certainly overnight, depending on the size of the battery. That flexibility is the point. A standard 10 amp socket adds roughly 100 km overnight, enough for a short commute but not for a big day, and it leaves no headroom. For times by car size, The Conduction Company's guide to how long it takes to charge an EV at home in NZ breaks it down.
One thing to ignore. If you have read that a 32 amp charger needs a 40 amp circuit, that is an American wiring rule: their code limits a continuous load to 80% of the breaker rating. New Zealand's wiring rules do not work that way, and some AI search answers currently tell New Zealand homeowners the American rule applies here. It does not. Under AS/NZS 3000 the breaker cannot exceed the cable's rating (clause 3.4.4), and an EV charger gets its own dedicated circuit rated for at least 32 amps, with an RCD that can detect DC leakage and an isolating switch beside the charger (clause 7.9.3.3). What The Conduction Company checks before fitting one is whether the whole house can carry a steady 32 amps on top of everything else. WorkSafe's 2026 guidance says a charger over 20 amps should have load management so it cannot overload the home wiring.
Do I need a permit or sign-off for a home EV charger in Auckland?
Not from the council, in The Conduction Company's experience. A standard home EV charger install in Auckland does not typically need a council permit. If your property is not a standard case, ask us before you book and we will tell you what applies.
The sign-off you do need is electrical, and your electrician provides it. Under the Electricity (Safety) Regulations 2010, a certificate of compliance must be issued for this class of work (regulation 65), and only a person authorised to certify the work may issue one (regulation 68). The regulations also require an electrical safety certificate from the person who completed the work, confirming the installation is safe to use (regulation 74A). The Conduction Company issues that certification on every EV charger we install. It is the document that shows the electrical work meets the building code, and in our experience it is the paperwork your insurer will ask to see. The Conduction Company's guide to electrical certification explains what each certificate covers.
Can a normal electrician install an EV charger?
Yes. A registered electrician can install an EV charger, and it is well within their normal work. In The Conduction Company's reading of the Electricity (Safety) Regulations 2010, adding a charger to an existing home installation is general prescribed electrical work, not high-risk work. You are adding a fitting to the installation. The electrician works at the switchboard, but that is not mains work, and mains work is what the regulations class as high-risk and require an independent inspection for (regulations 6A and 70). So no third-party inspector is needed. A registered electrician installs the charger, certifies it, and you are away.
The Conduction Company installs EV chargers across Auckland with our own registered electricians, and our director Jordan Statham is a registered electrical inspector as well, so if a property does turn out to be a special case we can tell you before anyone picks up a tool.
Frequently asked questions
What is the 80% rule for EV charging?
Charge your EV to about 80% for everyday driving, and keep it above 20%. Nickel-based lithium-ion batteries last longer inside that band, and sitting at 100% every night wears them faster. The Conduction Company's advice to Auckland clients is to set an 80% limit in the car and leave it there, then raise it to 100% only for a long trip. LFP batteries are the exception and should be charged to 100%.
Is it bad to charge an EV to 100%?
Not as a one-off, and not at all if your car has an LFP battery. In a nickel-based car, charging to 100% before a long drive is fine and does no measurable harm. What wears the battery is sitting at 100% every night when you do not need the range. The Conduction Company's rule of thumb is 80% for daily use and 100% when the trip calls for it.
Is it better to charge an LFP battery to 100% or 80%?
100%. LFP packs (every BYD, the MG4 Standard Range, and the rear-wheel-drive Tesla Model 3 and Model Y) are designed to be charged to 100%, and Tesla and BYD both say to do so at least once a week so the range gauge stays accurate. The 20% to 80% habit is for nickel-based packs. If you are not sure which you have, The Conduction Company's advice is to check the charging screen or the manual before you set a limit.
Why does my EV lose range in winter?
Because a cold battery cannot give up all of its energy until it warms, and the cabin heater draws from the same battery. The energy is not lost, it is temporarily unavailable, and the heater is the bigger cost. Recurrent's 30,000-car study puts the average EV at about 78% of its range at freezing point. Auckland rarely gets that cold, so The Conduction Company tells clients to expect a smaller dip and treat it as normal.
What qualifications do you need to install an EV charger in NZ?
A registered electrician. Installing a home EV charger is general prescribed electrical work under the Electricity (Safety) Regulations 2010, so a registered electrician can do it and certify it without a separate inspector. The Conduction Company's electricians are registered, and our director is also a registered electrical inspector.
Do I need a council permit to install an EV charger at home in Auckland?
Not typically, in The Conduction Company's experience. The sign-off a home EV charger needs is the electrical certification your electrician issues under the Electricity (Safety) Regulations 2010, which is a certificate of compliance and an electrical safety certificate. That is the paperwork that shows the work is safe and meets the building code. If your property is unusual, ask The Conduction Company before you book.
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