Hi, I’m sure, that there were topic about it, but i couldn’t find answer, so please point me to the topic if it exist 
I bought 21700 unprotected battery, because, you know… the name of this battery is their length and width… But yeah, they are shorter. Is there a way to fit it? Maybe even some clean solution?
Welcome teweyjir!
There are several ways of making a ‘button top’ from a flashlight. For example, I’ve posted a simple way here in this topic: 【convoy】 - #16390 by Wingman
This is a really easy way, without much risk and not much skill needed. You gain some length and it makes it a button top.
There are a couple of other ways, but they all have some downsides:
-First of all, you can buy seperate buttons, for example on Aliexpress, but you also need a battery spotwelder that is powerfull enough and it takes some practice to make sure you make good quality welds.
-The second way is to solder a ‘blob’ on the positive terminal, but that might introduce quite a bit of heat into the battery and a lot of people aren’t a fan of this technique.
-Some people use small round magnets on the positive terminal of the battery, but there is a risk that it may shift and in the worst case could short out the batteries, with all the troubles that could bring.
So personally, I would go for the technique I mentioned first in that other topic, because it’s relatively easy, not too expensive and when done right, not much that could go wrong.
EDIT:
Here you can find those ‘spacers’/adapters that I used:
Make sure to select the 21mm in your case. 21700 attery wrappers/sleeves can be found in all kind of places, but certainly on Aliexpress there is choice (in colors) enough. Be aware though that they need to be carefully heated to get them to shrink propperly and evenly.
EDIT: @Qubeet beat me to it! 
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How short is your battery ? If it’s 1mm shorter than 70 mm I doubt it makes any difference.
What type of battery is recommended by the flashlight’s manufacturer ?
UPD: the spacers, suggested by Wingman
it’s 5mm shorter:
Okey, I forgot about spacer. Yeah. It looks like the way to go! Thank you very much!
How tall is the spacer from Convoy? If it’s 2 mm then one should be enough, shouldn’t it?
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I measured it and the spacer was ~2,54mm. I’ve seen on Convoy’s site that the design is slightly changed (PCB looks a bit different), but I doubt that the thickness has changed much.
By the way: on your photo you compare a regular unprotected flattop, with a 21700 with build in charging (and protection), which are always ‘longer than normal’. Does the flashlight has springs on both sides? And have you already tried if the unprotected battery makes good contact? The springs can normally compensate quite a bit for the length of the cell.
Most likely the unprotected cell is still around 70mm (± 1mm) long and that protect fenix cell, could easily be 74mm. (And for some flashlights that could even be too long.)
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I tried. It flies inside xD. If i shake it fast enough it starts shining
It only have one spring, I’ll order the spacers when the website starts working
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Hmmm, that’s a shame! There is a big chance that the long Fenix battery (that you show in the photo) has permanently compressed the spring, so it will not reach it’s initial height. The fact that only 1 spring had to absorb it, doesn’t help either.
I hope that the space will be enough to get a good connection. The only other thing I can think about, is getting a new (tail) spring which has more height, but that also depends on how the spring is mounted in the tailcap.
Out of curiousity: do you have a digital caliper? If you, can you measure the exact length of both batteries? If you have a metal caliper: BE CAREFUL to not short out your battery and place a small/thin pies of tape on one or both sides of the battery, to prevent a short.
If you don’t have a digital caliper, can you tell me what brand and type that unprotected (blue) battery is? That way I could look up de manufacturers specs.
I’d guess your new cell is a regular 21700 and the Fenix cell is longer than 21700 specs due to the built in charging.
I’d also reccomend those convoy cell spacer things, if the gap is too large, just stack two together and heat shrink them together.
You might also find that low temperature solder could be used to solder those spacers together on a heatplate before heat shrinking them, not sure what the temperature limit of the PCB material is though…
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That is because it is Not Protected. It is the Wrong type to use in a Fenix, as they REQUIRE a Protected Battery.
Making the UnProtected battery longer is not a good solution, because the battery will still be UnProtected. This is a Safety Risk!
Which exact make and model of light do you have?
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How are you going to charge the new battery?
Make sure whatever added length you fit will accommodate your charging system.
If you don’t necessarily need a button I don’t see why a magnet on the tail end wouldn’t be a simple quick solution. Just small enough to fit inside of the wrap.
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Just my ignorance/lack of knowledge, but do (some) Fenix flashlights don’t have LVP and/or reverse polarity protection? A protected battery should could/should be enough by itself, but I rather have the redundancy of having it also in the flashlight itself.
Good point; having it on the tail end wouldn’t be a problem indeed. In my mind I had the picture of some people that use them to create a button on a flat top, but in this use case, it doesn’t need to on that side indeed.
correct.. some Fenix are sold with Protected Batteries for that reason. They then list the light as having protection, which actually is because it is the Battery that is protected.
but rather than speak in broad generalizations.. OP should be Specific about which light he has.
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Sorry for late reply, I didn’t check the inbox. I ordered 10 pieces of spacers and I’m waiting for them to came.
I thought about it, but It’s impossible and not worth the effort to change the spring.
The battery is:
SAMSUNG INR21700-50E 5000mAh Li-ION 3,7V
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yes, I know and I don’t care. The price of 2 batteries is lower than new light.
Fenix E35
I have charger from Fenix model: Fenix ARE-D1
No problem as the charger is for protected cells
Because i tried. You mean normal, flat magnet? If so, I tried with two magnet which i took from fridge, but none of them worked
Often people will put a small magnet on the positive contact to turn a cell into a “button top”. This is dangerous as outer case of the cell is the the negative contact, and connected to the body of the light, if the magnet shifts and bridges the positive pole of the cell with the body, this is a short circuit.
The spacers method, especially when heatshrinked, looks like it will be much safer.
Is the magnet sitting on top of the shrink wrap? If so it’s not going to make contact with the battery.
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I dont mean a risk to the light,
IF you overdischarge an UnProtected battery, there is a risk of Fire during recharging
Be sure you supervise during charging. Do not charge while you are sleeping.
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Have you considered just stretching the spring to make it 5mm longer? I don’t own an E35, but from what I see on the internet it appears to be a spring that could easily be elongated: 1lumen Fenix E35 v3 Review
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