The obvious questions:
Have you tried the button tops and have you tried protected button tops?
Some lights are designed to only accept protected cells.
Where do you get them and what size for the 18650s?
Its a diving light.
Cheap but solid and very bright.
I am using button tops.
Standard Panasonic batteries but the light comes with some generic brand battery that is longer.
I just checked their website and their batteries are protected.
The lights are only $50 so I am going to stick with my Panasonic standard batteries.
I have one of their video lights and they work in them for some reason.
HKJ says Test / Review: NCR18650A protected (Green) that the panny ncr18650 protected he tested were 69.7 long how long are your “good” ones?
My batteries are not protected.
I have said that already.
Well, all you need to know is written in the first answer.
If you would measure your batteries, you could find out, if they are maybe fakes?
Not home ATM but they are legit as far as all the reviews on Amazon (and weights) go.
Protected batteries are longer or the same length?
Longer, because of the little protection-circuit.
They are 2-3mm longer.
You can use a magnet or just a little piece of metal - just make sure it doesn’t short out the battery!
ANd maybe you could contact the producer, what he sais about that.
If you can solder but just aren’t comfortable soldering to the battery, I suggest you replace the spring with a longer one. It makes it easier to swap batteries than a small magnet would permit. (IMO)
Protection always adds length for the protection circuit.
Yep they must be closed today.
Usually they are good with CS.
Not sure I can access it as its a long way down and a diving light so pretty well sealed.
The magnets might be the best bet then.
Anyone have a link or know which ones to buy off Amazon?
And do you just throw it down the barrel before you put the battery in?
You attach it to the bottom of your battery then insert the battery + magnet into the light. Something around 16mm x 2 or 3mm thick should work.
I don’t have a amazon link but how about fasttech? 15*1.9mm Neodymium Magnets 10-Pack $2.28
If you are using the magnet on the positive end of the battery just make sure that the magnet doe not come into contact with the flashlight body itself from a knock or other reason. If the negative and positive are joined together it creates a short with bad results. If you are unsure about anything it maybe safer to use longer cells. Saying that I have used magnets in the past, just carefully. All the best in your quest. 
Awesome thanks for that.
Cheers mate.
Electrical tape should do the trick.
Thanks for the tip.