Mild Hybrid doesn't run in electric mode.. it's a very small electric motor and battery. In most cars, it's really just an electric stop-start. In a few, it adds a couple.of horsepower to help with acceleration. In any case, it has no real benefit to the driver; it's just there to improve MPG and rescue carbon emissions under test conditions.

This is the one where there seems to be most confusion over, certainly going by comments I read on the forum. Even with some regular members (who I'd assume to know better) I've read comments like, "mild hybrid wont drive very far on electric power". As you say, a mild hybrid (MHEV) won't drive any distance on electric power alone, though it may coast for a bit with the engine off and the engine may switch off as you slow to a stop.

In ascending order of electric power you've got:

MHEV, mild hybrid electric vehicle(!). As mentioned above, this will not drive anywhere under electric power alone, though you may get some engine off coasting and/or slowing down.

HEV, hybrid electric vehicle. This is a self charge hybrid like the Yaris, capable of driving up to a couple of miles at a time on electric power. The battery recharges very quickly, so rather than thinking about how far it will go under electric power, think about how often. Thats why, for someone who does most driving in urban environments, the benefits can be very large.

PHEV, plug-in hybrid electric vehicle. This will have quite a big battery and some examples can drive more than 30 miles under electric power. Obviously (as the name implies) they need to be plugged in to recharge (though they will recuperate power through braking the same as an HEV, with such a big battery the percentages gained are very small) and they are also very expensive.

EV, full electric!

More confusion also comes directly via the manufacturers who bandy about terms like "hybrid technology" (in reference to MHEV's) and often have badges on the car saying so. The cynic in me says that this is simply because the term "hybrid" sells cars and people latch on to it. They buy MHEV's and assume it is the same as an HEV when it isn't. While it is a bit of a con, it isn't that much, because it isn't actually hard to find out whether the car in question is MHEV or HEV if the person can be bothered to look it up.

But it is also completely pointless to pontificate between a solely ICE car and MHEV. If buying new you don't have the choice, and if buying used just go for the youngest version you can afford and ignore whether or not it is MHEV.

The battery spec will reveal the type of drivetrain...

Mild hybrid - basically just gives regenerative braking. 48V 10Ah-20Ah (0.5-1kWh) battery. Usually works via starter-generator on serpentine belt. Unless you drive a lot in stop start traffic it will make sweet FA difference to you. Never runs on the electric motor. You are dragging around an extra battery and heavy gen/starter and there is added complexity. Not worth bothering with for 80% of drivers but helps VMs meet emissions and economy targets.

Hybrid - Typically a 1-2kWh high voltage battery (e.g. 200V). Can drive very short distances on electric only. Again, its really just braking energy recovery. Savings in town but nothing meaningful in rural/highway driving.

PHEV - As hybrid but battery 10-20kWh with external charging socket. Can cover typically 20-40 miles in EV mode on a charge - enough for a commute. Pretty useful IMHO.

BEV - no ICE. Battery usually 40kWh and up.

There are also slightly oddball systems such as Mazda i-Eloop, which is a kind of very mild hybrid which delivers almost no fuel saving but lumbers the owner with some potentially very expensive to replace parts.....

Incidentally, to needlessly correct a previous comment, the Honda CRZ is full Hybrid and manual.

The CRZ may be classed as a HEV, but in reality it is more akin to a MHEV+. While the hybrid system does add something like 15bhp and about 90NM of torque, it won't run on electric only. The electric motor will only assist the ICE (like a MHEV).

This does all seem to be more confusing that it should be - well to me anyway. I'm thinking we might try and condense it into a Sticky thread.

Seems to me that the confusion is mainly surrounding MHEV and HEV

Also that a big chunk of that confusion is caused by the way these different types of hybrid are marketed, named and badged by their respective manufacturers. I think the main thing to do if you are unsure of what type a car you are looking at has, is to look it up (or ask on the forum).

But unnecessary confusion is added by some of the comments further up saying that MHEV should be avoided in favour of solely ICE. If, for example, someone has set their heart on a Suzuki Swift no older than the 2020 facelift, they are all MHEV. So the question of whether MHEV is worth bothering about is in itself not worth bothering about!. Same applies to quite a lot of other cars, you either can't get one which is solely ICE, or if you can, it will be a lower powered version (such as the Fiesta, where the 75 and 100bhp versions are ICE, but the 125 and 155bhp versions are MHEV only)

Ignoring that, there also seems to be a lot of ill informed opinions on the extra weight a mild hybrid system adds, which is only in the region of 25-30kg. The effect of this on overall mpg would be negligible and certainly well under 1%, whereas the average mpg gains from a mild hybrid system start at 5% (when What Car put a MHEV Suzuki Ignis through their real mpg cycle, it showed a 15% improvement over the solely ICE version they'd tested the year before)

No weight gain is insignificant as far as fuel consumption goes - hence why car makers have been reducing fuel tank sizes and ditching spare wheels to save a few kilos.

Only if you are naive enough to believe that is why they are doing it (rather than to reduce costs and increase profits).