Before you buy a used car, what is it you really need to know? I mean, we do try our best at Autocar and tell you what tyres to kick, which things to tap and what you ought to be worrying about. The thing is, that’s not really enough. Mostly, ‘what to look fors’ can be very deceiving.

What we need is a book. No, let’s be modern: an interweb site. Nope, that won’t do, either. These days it has to be an app - an app that rates a used car’s repairability. Because we really do need to know whether the car we are about to buy is not just easy to live with but also to fix.

Of course, you can just throw money at a problem, but that can prove to be ruinously expensive. I mean, all we need is a graphic of little spanners to explain the level of difficulty of, say, changing a battery.

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I’ll use the battery as an example, because of an email I received from an Autocar reader on an unrelated subject. His 2002 Porsche Boxster requires something of a procedure to get access to the battery. That’s because the genius designers at Porsche imprisoned the battery behind an electronically actuated boot release.

Apparently the factory fix if your Boxster won’t start is to attach some jump leads to the fuse box in the passenger compartment. But that doesn’t work if the battery is as flat as a pancake.

The next battery crisis involved a mate and his Ford S-Max on holiday. When the battery went, he bought a replacement and planned to do the swap by candlelight with a couple of spanners. Imagine his shock and disappointment when he found an airbox in the way. It was an almighty faff to remove, or rather slide the battery out, and it took over an hour and a half. To change a battery. That’s ridiculous.

I suppose this is what contemporary cars have come to: complication. It isn’t what we need right now, when, as we all know, changing a bulb involves a ramp, the removal of a large piece of plastic bumper and then 10 minutes on a laptop telling the car’s computer what you’ve just been up to.

It’s bonkers, but it wouldn’t be with a Bangernomics fixability app. After a few taps, you’d quickly discover that the motor you want is fixable, like an E38 BMW 7 Series.

Yes, I was very pleased with myself recently when I changed an ignition switch with a £10 part from a scrappie. The other year I even changed the battery in 10 minutes. So come on owners’ clubs and forums, home mechanics and Autocar readers, start rating your rides. Then we can wrap all that information in an app and make the world a better place. I think.