Hybrid car technology is in the middle of going from niche to mainstream.

And we’re going to be hearing more about it in the years ahead, especially as the automotive industry aims to meet more stringent vehicle emissions regulations.

We are also going to see a rapid increase in the number of plug-in hybrid vehicles – for the same reason, to trim fuel use to new lows to satisfy government requirements.

So we thought it was a good time to revisit the key differences between hybrid and plug-in hybrid technology.

For starters, not all hybrid cars (or hybrid systems) are created equally.

We’ve done a story on the different levels of efficiency of various hybrid cars before. You can read all about it here.

But if you don’t want to lose your place in this story by clicking the link, in essence Toyota’s hybrid technology is the benchmark (it slashes fuel use by about 50 per cent compared to a conventional petrol car).

The latest hybrid tech from Hyundai and Kia is pretty good too (about 35 to 40 per cent more efficient than its petrol-only models, in our testing).

But the current hybrid systems of other car brands (such as GWM Haval from China) only trims fuel use by about 25 per cent – and the current Mazda and Subaru hybrid tech delivers zero discernible difference in our testing.

With that recap out of the way, here is the nub of this story.

Regular hybrid cars have a small electric motor and a small battery pack that recharges on the move while you’re driving (such as when you’re braking or driving downhill).

You do not need to plug them in. That’s why it’s genius technology and it’s also why they’re so popular.

On a hybrid car with good tech (such as Toyota which has been leading the way on this for more than 20 years) the electric motor moves the car from rest (such as at a set of lights, an intersection or stop-start traffic) up to about 40kmh.

Once the hybrid car gets that free propulsion from the electric motor to 40kmh (or thereabouts), the petrol engine takes over.

Moving a car from 0 to 40kmh (or thereabouts) is the thirstiest part of driving because you need a lot of energy to move a car from a standstill – but less energy to keep its momentum above 40kmh.

That’s why good hybrid cars are so fuel-efficient. The brands with less efficient hybrid-car technology are working on new systems to try to match Toyota’s fuel savings.

So, what’s the difference between a regular hybrid and a plug-in hybrid?

As the name suggests, with a plug-in hybrid car you can plug it into a power socket to get some extra charge.

Plug-in hybrid cars have a bigger battery than regular hybrids (hence the need to plug them in) and have bigger electric motors (to deliver more oomph).

Most plug-in hybrid cars to date have a battery pack that can enable the car to be driven on electric power alone for up to 50km in ideal conditions (before the petrol engine takes over and delivers another 400km or more of driving range).

Chinese car giant BYD has reset that benchmark with new plug-in hybrid tech that delivers up to 95km of electric driving in ideal conditions (before the petrol engine takes over) and more than 600km of petrol driving range (according to the claim).

For many plug-in hybrid buyers, they may be able to commute daily and not use a drop of fuel – if they are diligent about charging the car.

But here’s the thing. A lot of owners of plug-in hybrid vehicles (or PHEVs in the parlance) don’t charge the battery, and so they end up driving around on petrol power the whole time.

And guess what? In this scenario, a PHEV uses as much or even more fuel than a regular petrol car because it is carrying the extra weight of the battery pack and electric motor.

So the main takeaway from this is: for now we still reckon a normal non plug-in hybrid is the way to go for most buyers looking to save money and save fuel, especially if it’s a Toyota hybrid.

The price premium of a hybrid car versus the equivalent petrol-only car is modest, and if you buy a Toyota, Kia or Hyundai hybrid you will save 35 to 50 per cent on fuel. And you don’t need to remember to plug it in.

However, if you have somewhere you can charge a car from a normal power socket at home or at work, a plug-in hybrid could be a good option.

But be sure to charge it at every opportunity.

Plug-in hybrids (for now) don’t have the same level of fast-charging as electric cars.

For example, to top-up the BYD Sealion 6 SUV or BYD Shark 6 ute (both of these plug-in hybrid models share the same 29kWh battery pack) from empty would take about 15 hours on a household power socket.

So you really need to stay on top of it, otherwise it becomes a petrol car carrying around an electric motor and battery pack that’s not in use.

And we know this happens. We’ve lost count of the number of times car wholesalers have told us about trading-in PHEVs only to find the charge cable still in the original wrapping in the boot, never used.

In the end, both hybrid and plug-in hybrid cars are going to become the norm in the years ahead because it’s the only way to meet new emissions targets.

The curious thing about plug-in hybrids is they have a super-low fuel rating on the mandatory consumption label – but there is no law that says the customer must plug the car in to minimise fuel use.

One final thought: if you have the diligence – and ability – to recharge a plug-in hybrid car regularly enough to stay on top of it, why not just buy a fully electric car?

To find out more about the pros and cons specifically on plug-in hybrid cars, here is an article published previously by EFTM.