Simple, Cheap, Cool, Waterproof and Gummy Diy Battery Holder

I know how many of you inventors have desired a versatile battery holder to power your projects, I know you can't sleep without that... so this strange accessory has born ;-)
This gadget has a simple function, keep a battery inside, and yes you could buy an ordinary plastic black and impersonal battery holder if you want, but keep in mind that this is coloured (you can choose the Sugru colour that you prefere), rubbery and even water resistant (although you can't dive with it...).

I made it for Li-ion 18650 batteries, because they're very powerful and really versatile for electronic projects, but you can build the same gadget for one or more batteries of any type, voltage and shape.
I've used some metal washers to make contacts, maybe copper pieces should have been better because copper is more conductive... I'll let you know after some test.

To choose the right washers you have to give a look to these two images. As you notice the fat washer can't make contact with the negative side of the battery, so we'll use it for the positive terminal. Same matter for the thin one, theoretically it shouldn't touch the positive tip so we'll keep it for negative flat side. Pay attention to avoid any shortcut when working with powerful rechargeable cells, it could be danger and damage your batteries.

Let's melt some tin on the washers. Probably you should find it very arduous because tin doesn't stick on the steel of the washers, in that case it's essential spread some flux on them.

Now you can choose some good quality natural rubber bands (better with flat sides, not as mine), the more they're tense on the batteries, the more they'll keep the contacts connected. You can try with only one band for each battery if it's enough strong.

To keep the bands in place meanwhile you work on the batteries ends, wrap them with some tape pieces.
I've covered the battery ends with some silicon grease, to avoid the caps attaching to the batteries surface, but I'm not sure it's the best material, it worked not very well... maybe some oil is better? Some Sugru guru certainly has the answer.

Now the best material to wrap the washers and keep them over the batteries ends it's the Sugru, because it dry fast and it has all the colours you want, you can indeed mix the basic colours to make the full rainbow! Another solution could be the two elements silicon which I've used to make the remote control plug, but it's ugly pink!
We choose obviously black and red packets from the five colours of the set, we don't need to mix this time.

Now cut in half each packet's content, stir it in your hands and cover the washers on the right sides of the batteries.
Then push it around the cilynders, and over the washers so that it will englobe them. Finish off the external surface of the Sugru (maybe better than I've done), and hung them up to avoid leaving a flat print while they dry. 
After some time (maybe one hour to be sure?) you can pull the two caps away from the batteries and clean them.

It's all! You have now two new battery holders which could be useful to power some little electronic project, or maybe your phone or your digital camera too (usually cellphone and cameras li-ion batteries have one cell, so the same voltage of 3.7V 18650 stilo), all with some dedicated plugs to connect at the wires ends.