If you’ve purchased a number of combustion engine cars over the years, you’ve probably got some idea of the kind of questions you’d want to ask. What’s the gas mileage, service interval, oil change frequency, and a few other details that give you some idea about the longevity and running costs of the vehicle.

But of course not only do many of these flat out not apply to electric vehicles, there are some important questions that need asking before you commit to making the switch.

So here’s a few things you might want to either ask or research before buying your first EV. Dealers on the whole are not clued up too well on electric vehicles so if they can’t/won’t answer any of these you’d do well to research them independently.

Does the battery have a Thermal Management System (TMS)?

One of the things that damages batteries of all kinds is heat stress. When you charge and discharge a battery the temperature change can cause physical and chemical changes within the battery that shorten its usable lifespan. Considering the battery is the most expensive component in an EV you want to make sure that it lasts as long as possible.

The job of a TMS is to regulate the battery temperature, making sure it never gets too hot or too cold either while in use or while being charged. By keeping within the ideal temperature range not only does the battery last longer (batteries equipped with a TMS experience virtually no degradation even after many years and huge numbers of miles) — but it also allows the battery to be charged at its best speed. A battery that is overheating or too cold cannot be charged at full speed.

If the car doesn’t have a TMS then you may find for example that if you make multiple charging stops on a long trip then each charging stop takes longer, as the heat buildup means the car has to slow down its charging rate to try and protect the battery. Cars that actively manage the battery temperature don’t have this problem.

What is the battery warranty?

Unlike combustion engine vehicles, electric vehicles often have separate warranty terms that cover the battery specifically. This may be a given distance travelled, a period of time, or both. The more generous the warranty the more certain the manufacturer is that the battery will not degrade during that time. The warranty will also usually state a given capacity at which the battery is considered ‘degraded’ — often 60–70% at which point the warranty kicks in.

Also consider whether or not an extended warranty is offered. If one is offered at a reasonable price then it’s a sign that they’re confident the battery is unlikely to expire outside of the initial warranty period either.

This needs to be taken into consideration with the first point as well. If the warranty term is short, lower distance with no extended option and there is no thermal management — this is a sign that the manufacturer is less than confident in the longevity of their battery pack. Doubly so if the dealer is especially pushy about trying to get you to lease the battery separately from the rest of the car, and steer clear of any that flat out refuse to let you buy the battery outright as part of the car.

What is the maximum speed for AC and DC charging?

Most new electric car models being released today and over the next few years support a charging standard called CCS (Short for Combined Charging System) — CCS as a standard is nominally capable of charging rates of up to 350kW (the older version maxed out at 80kW but is forwards and backwards compatible) but no charging stations available today are capable of that level of output, and most cars aren’t capable of accepting that level of input.

A complete rundown on all of the charging systems that are available and their capabilities is worthy of a separate article all to itself, but the important factor is the rate of charge.

Needless to say, the higher the charging rate — the quicker the car will recharge. Broadly speaking DC charging is used for Rapid charging (Typically around 30 minutes) and AC charging is for standard rate charging such as you may use at home or in car parks, taking between 4 and 12 hours depending on the car and charging speed.

As of time of writing (June 2018) the fastest DC rapid charging rate of any EV on the market is 120kW (The Tesla Model S and Model X), and most other EVs run at about 50kW peak. For AC this typically runs at between 7 and 22kW. If you’re on the lower end of that you’ll want to avoid using the AC connection on a ‘rapid’ charger and instead either use its DC charger or in the case of a PHEV keep to non-rapid chargers whose output is similar to what your car can accept.

The other thing to consider is that the battery won’t charge at a constant rate, a nearly empty battery can charge extremely quickly but a nearly full one won’t accept any more than a trickle. So it may be worth finding out what that curve looks like. This isn’t something the manufacturer will likely know or show you so you’ll need to talk to owners to get some idea of what the real world curve looks like.

Some cars such as the Renault Zoe lack DC charging entirely, and instead use an unusually fast AC charging system, the Zoe is unique in using a 43kW AC charging system through its Type 2 socket.

What is the per-mile (or per-kilometer) energy usage?

There’s a few ways to measure an EVs energy usage, it’ll either be in terms of watt-hours per-mile (wh/m) or per-kilometre (wh/km), or in terms of kWh per 100km. In all cases the lower the better. This will tell you how fast you get through the battery.

Depending on the size of the car, the driving conditions and how you drive it — you’d expect an energy usage of between 250-400 wh/m. This equates to ~155–250 wh/km or 15.5–25 kWh per 100km. The lower end being smaller city cars and the higher end for SUVs.

The lower this number the less frequently you’ll have to charge and the further you can go for any given battery capacity. You may also want to consult with existing owners to see what their real world energy usage is in various conditions. EVs tend to consume more energy when it’s very cold so if you live in a colder climate this is definitely something to consider. You can often expect a 20–50% increase in energy consumption (especially for short trips, long trips are less of an issue) in cold weather below about 5°c.

What is the actual usable battery pack capacity in kWh?

Many EV manufacturers advertise the capacity of the battery in terms of the raw pack capacity as measured in kWh (kilowatt hours, 1 kWh is the equivalent of 1 ‘unit’ of energy in your home energy bill).

However most batteries ‘reserve’ a certain amount of their capacity that can never actually be used for driving. This acts as a buffer that helps to protect the battery as Lithium based batteries shouldn’t be fully discharged for extended periods as this can damage them. This is a reasonable and important safety and longevity feature.

So it’s worth checking out how much of that capacity is actually usable to you for driving. Typically about 5–8% of the battery capacity is reserved for this purpose but it can be bigger. Some manufacturers also use extra ‘padding’ beyond what is needed for safety to help improve the longevity of the battery.

In attempt to push for a ‘bigger numbers is better’ situation some manufacturers (namely BMW) advertise the pack capacity in amp-hours (Ah) — in terms of usable battery capacity this isn’t that useful without knowing the pack voltage as well (watts = volts * amps) so push hard to specifically get the figure in kWh to let you easily compare it to other cars you may be considering.

Wait, why not ask the range?

Because in practical terms the question “How far can this car go?” is fairly meaningless. The answer depends far too much on factors like the temperature, the elevation change between your start and end point (uphill of course uses more power than downhill), how much your trip consists of stop/start v.s. cruising, speed of travel and your personal driving style. A given range that assumes cruising on a flat road at a given set speed and temperature won’t actually be that meaningful and two different drivers in two different situations can get massively different real world results.

So instead you want to look at the power usage and battery size, seeking as low as possible for the former and as high as possible for the latter — and this will get you the best range.

If you do want to ask about the range, take the answer with a pinch of salt. In the EU the NEDC figure is often given which isn’t even remotely useful in terms of real world driving habits (it’s equally useless for realistic emissions levels for combustion engine vehicles). In the US the EPA figures are more useful and aren’t a bad starting point as a rough idea, but again specific circumstances can have huge impacts on the usable range of any vehicle.