you should not make your own batteries, they are dangerous if not made correctly. You need a spot welding machine, PVC tubing, heat shrink machine, kapton tapes, silicon wires, high power soldering iron, solder, flux, cell holders, metal strips and load tester to make a safe battery. You also need to buy a suitable BMS and a charger besides recovered laptop lithium cells.
Motor kits are plenty and cheap on ebay.There is no way you can save money on a cheap 8-Fun kit by buying separate components and put the kit together yourself.
There are plenty of cheap e-bikes on the market, sold at prices that make home build inefficient: Halfords Coyote, Tesco Hopper etc. After you know what you ideally want (and that's likely expensive, the kind of bikes that cost more than £1,000), then build your own to save some cash. You won't save much more than £200 on a £1,000 bike. Even then, choose a well proven plug and play kit for your first conversion.
Time to write is 22:12pm, finish at 23:39pm. Means, 37 minutes to write this reply on date, 21st Thursday, 07 July, 2016 pm.
Thanks very much for giving battery advice on not make own batteries because of issues as lack of knowledge in comparison to companies that spend years and lots of money on tests to make sure each battery is safe.
Having said that big companies due to knowledge that allows batteries to wire together correctly to give the right electric that transfers each cells power together to be safe to use. Then, I have seen people on YouTube that make battery cells together in positive and negative rows with spot welder, cell chargers, battery management system, and heat shrink wrap to encase all the batteries together with years of experience as a engineer that the final battery is safe to use.
I read in your reply, many components that you give names for that more accurately get you search results for the right product. I am searching for when I look at the components using other names, products that are similar or a little bit different, yet still are correct. For example: I come across in a video, a material called heat shrink wrap, the link to my Google search is here:
https://www.google.co.uk/search?sourceid=chrome-psyapi2&ion=1&espv=2&ie=UTF-8&q=heat shrink wrap&oq=heat shrink wrap&rlz=1C1EJFA_enGB664GB664&aqs=chrome..69i57j0l5.5037j0j7. Heat shrink wrap I see in use is for to wrap up the battery pack to take heat for the battery pack to be cool and for the cells in the battery case to holder together better.
Now, the key difference with Kapton tape, I search for on Google, in your usage I think is for wrapping up battery packs. Kapton tape as name tells you comes in the tape form, this method of tape uses more strips to cover it all, and the strength of tape is less I find than a whole material like heat shrink wrap.
Thanks for all the other information such as, "spot welding machine, PVC tubing, heat shrink machine, kapton tapes, silicon wires, high power soldering iron, solder, flux, cell holders, metal strips and load tester".
With regards to saving £200, on a £1000 bike, that is still decent amount of money to save. A conversion kit is good as the price is a lot cheaper, can be had for £300 for 25 watt with battery and charger online, saving £400 from a £700 e-bike.
I have important work to do in following days and months, this means I am not returning, in the coming year to this forum. Although, I do value everybody's help to make e-biking from a designer or rider view a lot more enjoyable and educational to help drivers learn better how e-bikes work, or why certain e-bikes are better than others.
I have already given e-bikes enough of my time for research to find out how to make battery, own motor or to buy e-bike conversion kits and to purchase e-bikes instead. I think I am happy to say thanks for allowing myself to learn with everyone who gave effort in to helping myself learn more about e-bike laws, which e-bike to buy and how to make your own e-bikes.
Enjoy your time today, make tomorrow even happier, live well in your life with your loving family and friends, and have a good future, where you do better in your life to give the world good and love.