Cheapo jump leads - how to "improve" them and use them

Yup, you're better shelling out a few "bob" more to buy something with better, thicker copper cables and robust clamps.

People need to understand a basic fact about jump starting. Which is that most cars needing a jump to get going have batteries which are only discharged to the point where they won't quite turn the engine over. Anything which can raise the overall voltage by just a wee bit will enable the engine to crank. This is what these small capacity jump start packs are relying on. They have quite small capacity batteries which, as long as the vehicle battery is not too deeply discharged, can raise the overall voltage available by enough to crank the engine. As long as you appreciate they're not going to work if the vehicle battery is seriously "flat" then they do work well. Of course the smaller the jump battery the shorter period of time it'll allow engine cranking to take place.

If you haven't looked into "super capacitor jump starters" then this type may be of interest. They contain no battery (actually there's a "hybrid" version now which does have a small Li-Ion battery but we'll forget about them for now) The type which contains just capacitors work by using a bank of supercapacitors (seems to be 5 of them in most I've looked at) which it can connect together in either series or parallel. When you need to use it you connect it's clamps to the battery and set it to charge. It connects the capacitors in parallel so, as each capacitor only needs a few volts to charge (I think around 3 volts?) and your "dead battery" probably has at least 6 or more volts still available, It uses the "dead battery" to charge up the capacitors. Once charged, which seems to take less than 5 minutes, you press the activating button and the device now connects the capacitors in series which allows them to deliver around 13 or 14 volts which allows the engine to crank. It won't do this for very long but, as long as your only problem is a discharged battery, it'll crank it for long enough to get a start.

The advantages are many. There's no battery to remember to keep charged up. and there's no battery to degrade over time - projected lifetime of one of these is in excess of 10 years, a battery type will never last that long. Also, it's discharged while stored in the car so risk of shorts and battery fires is eliminated. If your battery is so depleted that it can't charge the device then it can be charged from another vehicle very quickly, or using a USB connector, but, in my experience it's going to be very seldom that you find a car with a battery showing zero volts, so real life conditions I believe it'll charge.

Anyway, here's a video about one brand - Autowit - but Sealey, Draper and others offer much the same product. Take a look at them, you will find it interesting I'm sure. https://www.youtube.com/watch?v=r7RMskdIWBE