Well, that didn't exactly turn out that way! But as our electronics have become more efficient, the cost of processing payments begins to outweigh the cost of providing electricity. How much would you pay to fully charge your smartphone? A quid? 50p? If you're desperate, a fiver?

A modern phone battery can hold about 22Wh (Watt-hours) of electricity. My domestic power provider charges about 13p per kWh (kilowatt-hour). So the energy in your phone costs less than half a penny.

If you have the latest Tesla, with the biggest battery - 100kWh I think - the total cost of electricity will be around £13. My car, the slightly more modest Soul EV, has a 30 kWh pack - less than £4 to fill from empty.

Given that most people won't be charging from 0% to 100% - and most merchants won't let you use a credit card for anything under a fiver - we can safely say that electric cars are too efficient to meter :-)

Except, that's not how the real world works. Use a litre of water at home and it'll cost you less than a penny - but buy a litre of water from a supermarket and you'll pay considerably more.

Why? Partly the infrastructure to supply you, partly the plastic bottle. Add in the advertising costs, staffing costs, insurance, and goodness knows what else - and you can see how expensive shop-bought water can be.

The same applies to supplying electricity for someone to consume. Even if you're just fitting a domestic plug socket, there's a labour cost involved, and the cost of periodic checks, and the cost of advertising that it is available. If you're supplying a rapid charger - 50kW as opposed to a domestic 7kW - there are some huge costs for equipment and supply.

For example, Electric Highway charges 30p per kWh to use their rapid chargers. But, even so, filling up from 20% to 80% is only going to cost a fiver. Once you factor in credit card fees, it's hardly worth collecting the cash. (And anyone who mentions a dodgy cryptocurrency being able to transfer funds instantly and for zero cost gets permabanned from this blog!)

So what are companies supposed to do? Broadly speaking, public car charging schemes fall into four categories.

1. Pay-as-you-go - with an inflated cost per kWh.
2. Pay-per-minute - sort-of makes sense if you're also paying for parking.
3. Pre-pay - top up your account by £X and pay per kWh from there.
4. Membership - pay £Y per month for unlimited charging.

For me, PAYG using a credit card makes the most sense. I mostly charge at home and don't regularly stop at the same charging station. I've used dozens of different charging schemes - here's a quick comparison.

Free! (ish)

I already had a standard 220V socket in my garage. My car came with a domestic charger. I plug it in when our solar panels are generating delicious free-range electricity from the sky gods.

Some public chargers are set to free vend. Usually in supermarket car parks. Electricity is a loss-leader; like cheap baked beans.

PAYG

This is the simplest method. Unfortunately, some schemes require you to pay using their app rather than just having a contactless credit card reader.

• 30p (15p if you're an Ecotricity customer) - Electric Highway
  • Uses a pretty rubbish app, but works fairly well.
• 33p - On street lamppost charging from Chargy
• 39p - Shell Recharge / Smoov
  • Tap to pay with credit card. Nothing could be easier! Read my review
• 30p + £1.80 connection fee - GeniePoint
  • prices vary depending on location and speed of charger

Pay by time.

I think this is a hangover from the cost to park usually being in time-based increments.

Pod Point have an excellent app, but a weird charging structure. Some are free, some cost 25p/kWh, some are £1 for 3 hours, and some change their cost throughout the day.

Pre-pay

A fairly annoying option - unless you always use the same charging network. I have a bunch of credit with various apps which I doubt I'll ever use again - and there's no way to reclaim.

• Polar Instant. £10 minimum top up, £1.20 connection charge. Some chargers are free, some cost £1.00 per hour, others are £6.00 for 30 minutes.
  • Verdict? Confusing, complicated, expensive. And the app is crap.

Membership

Are you a member of your local petrol station? No! The idea is ridiculous. You might collect bonus points from them, but why would you ever subscribe to them?

• £39 / month for up to 200kWh - On street lamppost charging from Chargy
• £68 / month for unlimited - On street lamppost charging from Chargy

If you have no charging at home, and can reliably use a lamppost near your home, this could be a decent service.

Worst of both worlds

Source London have a truly user hostile scheme. £4 per month, and then charging per-minute between 3.6p - 9.5p per minute - plus a surcharge in certain parts of London. Or you can pay a one off fee and the pay more per minute. Or PAYG.

Given the PAYG rates are only about 5p a minute more, you'd have to spend 80 minutes a month on charge to make it worth paying the monthly fee.

Confused? I think that's the idea!

What a mess!

Customers, mostly, don't want to interact with competitive capitalism. We aren't Homo Economicus constantly adjusting our behaviour to find the cheapest deal. We just want reasonable service at a reasonable price.

The infrastructure for charging electric cars is mostly here - but the infrastructure for charging money has a long way to go.

Straight up, it looks like a plastic toast rack. It's a chunky beast, but surprisingly lightweight. You won't have trouble lifting it, but it stays firmly in place.

Round the other side are 10 USB ports. Well spaced out, not too cramped.

It might be nice if they lined up with the rack, but that's a minor quibble.

There's a fan inside the unit, although I never got it to switch on.

Good airflow all round. It takes a standard "kettle" lead. I was happy to see a UK plug - complete with earthing - came with the unit.

Wired up competently, and with a 13 amp fuse. OK. Let's test drive this thing!

I thought I'd try and tip the unit over by placing a 10 inch Android tablet at one end. But the unit's centre of gravity is just right. Let's pile on the tech!

MOAR TECH!

The slots are just about wide enough for a MacBook Air to fit in.

EVAN MOOOORE TECHHHH!!!

2.4 amps is sufficient to power a Raspberry Pi. Imagine a Beowulf Cluster of those!

BUCKAROO!

Yup, the Nintendo Switch also fits.

OK, let's press the big button at the back and see if it explodes...

All the devices switched on. Those that support fast charging were able to draw the maximum current from it.

There is a fan inside the unit - to prevent overheating - but I wasn't able to get it to come on, even with all 10 devices charging.

Downsides

There's a lot to love about this mega-charger, but it isn't without flaws.

Firstly, it costs seventy quid. I guess £7 per charger isn't too bad - especially for a high power one. You also only need one plug socket.

USB-C devices are supported, but there's no USB-C specific slots. You won't get the advantage of USB-C fast charging. You can charge your new gadgets - but at slower speeds than with a dedicated charger.

Cable management is a bit horrific with 10 things plugged in. That's inevitable unless all 10 devices have a charging port in exactly the same place.

If I was going to be nit-picky, I'd prefer the USB slots to be spaced out in line with the "toast rack". It might be good to have individual LEDs for each slot.

Conclusion

If you've got 10 devices that you need charged simultaneously... This is probably as good as it gets.

You can buy the Ntonpower 10 port USB charger on Amazon.

So, thanks to some Amazon vouchers I got for my birthday, I decided to see how cheaply and easily I could get wireless charging working on my phone. Here's how I Qi'd up my kit for under £14.

The Receiver

If your phone doesn't come with Qi, you'll need a Qi receiver. A small circuit which can attach to your phone. Prices on Amazon range from £4 to £40. I bought a £6.49 one which also included NFC compatibility.

Attaching the Qi receiver was really simple. Pop the back off the phone, peal off the receiver's sticker, line up the contacts, replace the cover. Done in 10 seconds.

The Pad

Charging mats on Amazon range from about a fiver - up to £30. I picked a smallish one which also came with two extra USB charging ports for £7.

To charge the phone, simply place it on the mat. Then subtly reposition it until the coil is directly above the mat's charging circuit. Then try not to nudge the phone, lest you disturb the charging.

To be fair, the mat has a blue LED which illuminates once charging commences. The phone (depending on model) will also vibrate or play a sound to indicate that it's charging.

And, really, that's it. Deceptively simple. In an ideal world, every surface of your home would have an inductive charging loop built in. Throw the phone down on a desk or bookshelf and let it trickle charge whenever you're not using it. Just before falling asleep, it's much easier to place the phone on a mat than find and fiddle with a wire.

There's only one problem. It's slow!

Speed

This is the big fly in the ointment for Qi. It's perfectly suitable for charging overnight, or for when the phone is idle. It's not so good when you're actually trying to use the device.

Here's what a battery monitor reported the charging current as.

640mA really isn't very good. By contrast, when plugged directly into the official Samsung charger, the current is 1,800mA. Twice as fast basically. As I said, Qi is fine when the phone is idle, but 640mA is inadequate if you're using the phone.

For example, I also bought a Qi Car Charger, for £30.

In theory, it's great. I can just plonk the phone in the holder and not have to fumble for a wire. The problem is, I (legally) use my phone while driving. I've got Google Maps directing me around traffic and I've got my PodCast player streaming over Bluetooth. This means my screen is always on and the cellular and Bluetooth radios are working full time.

This power draw means that the battery just doesn't charge over Qi. Or rather, the charge and discharge rate are roughly the same.

Here's a typical reading from the power monitor. After an hour of commuting, my battery's power level hasn't appreciably changed.

If I'm lucky, the battery will have risen a percent or two over an hour. That's quite disappointing.

On the plus side, with this specific charger, the USB cable is easily accessible if I do want to charge directly.

Overall

The Qi Standard is pretty nifty. Wireless charging is surprisingly convenient for those occasions where you want to just place a phone down and not have to worry about whether the wire is USB, Lightning, or crocodile clips.

The physics behind this kind of inductive charging really do place some limits on the power levels which can safely be achieved. I've noticed my phone gets noticeably warmer when charging via Qi than by standard USB.

Qi receivers and transmitters are now very cheap - so hopefully we'll start seeing more phones incorporating this by default.