Converting Flat top batteries to button top

I apologize if this has been asked before.

I now own two 18650 flashlights. Both came with a pair of batteries (I tend to buy bundles). My Fenix PD35 came with Fenix branded batteries which are flat top.

My Eagletac S200C2 came with Xtar batteries which are button top. Well when the Eagletac showed up, I put the batteries on to charge, and then dropped one of the already charged Fenix batteries in. Hit the switch and nothing happened. Upon closer inspection it appears that the Eagletac is going to require button top batteries. However, one of the reasons I wanted to go with that light is so that all my flashlights had interchangeable batteries. So is there a way to convert my Fenix branded batteries to button top? Can I simply apply a dot of solder to the top? Or is there something I can buy to make the conversion?

Eagle

Hi,

Members have have conflicting opinions about this - take my opinion as that of someone who is very mindful of safety.

Do not try to add a solder blob to the top of the cell. Even if you use a powerful iron which reduces contact time, you may damage the PTC or vent slightly and you would have no way of knowing if you did or not.
Some people use a small spacer magnet but I feel this is dangerous because it would be easy for the magnet to slip and make contact with something it should not, shorting out the cell or damaging the light.
Button-top extender sleeves have been mentioned (and designs have even been discussed) but they would make the battery a very tight fit, and add extra contact points increasing the resistance of the circuit.

My recommendation is that you use the Fenix cells for the PD35 (and other lights accomodating of flat top cells) and use the XTAR cells for the Eagletac. In the future, try to buy button top cells where possible for maximum compatibility. This will keep you as safe as possible with minimal hassle!

Edit: Be mindful about cell length. Some button top cells are too long for some lights. Look for 18650 button top cells with the shortest possible length. I have had good success with the newer thrunite cells that do not have a side nickel strip (based on panasonic cells).

Thanks for the info. I was afraid you were going to say something like that.

Always happy to provide answers.

It's not all lost, there are many lights that take flat top cells. I know 100% compatibility is your goal but please don't compromise safety for that goal. I also have a few oddball cells that are for specific lights which is disappointing as I like to share "fuel" between multiple lights but its tolerable.

I have some experience with using rare earth magnets as button tops, and they have worked well for me. I carry a couple lights every day (I have a rotation, so they all get used), and actually USE them at least 20-45 minutes per day. They get knocked around all day on my belt, and dropped very occasionally while in use. Not once has a magnet budged from where I put it.

If the possibility bothers you, then just buy button tops to begin with (I generally do just that...but I try to match the best cells for a given light, and not every cell has an option of button tops, so I do have a few flat top 18650s). In my opinion, magnets are a workable solution...WAY down on the list of things you need to worry about.

Has anybody tried super gluing around a magnet on top of the battery to hold it in place, does the glue go under the magnet, the magnet would be pulling hard against the battery to hopefully it will not.

Clean parts with Alcohol before gluing.

John.

zipplet said:

Always happy to provide answers.

It's not all lost, there are many lights that take flat top cells. I know 100% compatibility is your goal but please don't compromise safety for that goal. I also have a few oddball cells that are for specific lights which is disappointing as I like to share "fuel" between multiple lights but its tolerable.

Click to expand...

Not going to worry to much. If the interchangability (or lack there of) is a problem I will give the Fenix batteries away and pick up another pair of Xtar. I think they are $6.50 or so online. $13.00 is not something to loose sleep over.

Eagle

I'd keep the Fenix batteries just for the PD35 now that you have to get other batteries you won't be tempted to wear one out between lights and always have a charged battery for the Fenix.

Idk but that's my thought.

Have a great day Eagle.

I don't see why a magnet wouldn't work just fine.The trick is to have some sort of insulating washer around it to prevent it from moving around.If you don't feel like a trip to the hardware store to find a rubber or fiber washer I'm sure you could cut your own from a milk jug or something similar.

TinderBox (UK) said:

Has anybody tried super gluing around a magnet on top of the battery to hold it in place, does the glue go under the magnet, the magnet would be pulling hard against the battery to hopefully it will not.

Clean parts with Alcohol before gluing.

John.

Click to expand...

Glue on outside circumference of magnet. This is exactly the same procedure I perform. Never had a issue. I did it with out the glue a few times. Had no problems in the light luckily, however when trying to remove magnet to charge a 26650 it slid to the edge and under the wrapper. Resulting in a nasty short. I slammed it down and got lucky it came off. After that I will either glue magnet or I put some 5 min epoxy around the top of the wrapper. Therefor sealing off any chance of the magnet going under the wrapper and shorting. Just make sure not to cover any vents either way you go!!
If cleaned properly, it only takes a small drop of glue.

I suggest not doing a Mickey Mouse conversion as it will be less expensive to buy new batteries compared to a battery that can cause personal/property damage if the battery malfunctions. I tried it, but my common sense told me not to do it.

I've never had a problem when using 5mmx1mm or 1.5mm rare earth magnets. I don't even use glue or washers or any kind of spacer, I just center them and load the whole assembly up. Most lights that need button tops have a non-conductive "protection" ring that sticks out and surrounds the magnet, so it's not going to shift anyway.

OK. So I picked up some magnets. The button top only flashlight is a car light for me. I plan on keep a couple magnets in the car that can be used in a pinch, but mostly will just ride along and may never actually get used.

zipplet said:

My recommendation is that you use the Fenix cells for the PD35 (and other lights accomodating of flat top cells) and use the XTAR cells for the Eagletac. In the future, try to buy button top cells where possible for maximum compatibility. This will keep you as safe as possible with minimal hassle!

Click to expand...

I agree, however I don't worry about trying to keep all one type of battery..........I just use the flat tops (panasonic NCR18650B's) on the Fenix and ArmyTek and the button tops on the EagleTacs, Nitecores, etc. Sometimes you can get the NCR18650B's for a good price over the protected batteries with button top. I have about a 50/50 split of both types of batteries.

What size magnet works best? Meaning the diameter. I see several different sizes, do they make a difference?

I ordered some 4mmx2mm magnets from Banggood. They will work, but I think 5mm would probably be a better diameter. I also found some magnets that didn't have a size, but the info claimed they were sized to be used with flat top 18650 cells, so I ordered some of those as well. I am waiting until those arrive to do my testing.

I use 5mm x 2mm Neodymium magnet disks. Very strong. They stay centered while installing the battery. I use them only on flashlights with polarity protection in the form of a non-conductive plastic ring at the positive terminal. Once the battery is in, the magnet is not going anywhere. I get them on eBay.

On the Samsung 30Q batteries, the positive contact has an air gap between it and the actual contact to the battery. Using correct preparation I have added my own home made soldered on brass button tops with a method that hardly heats the battery at all. Its all about preparation and method - as I solder small components as part of my work I have the correct tools to do this. However, if the battery does not have the air space, then it should not be soldered at all as it will be heating the mechanics of the battery.

thedoc007 said:

I have some experience with using rare earth magnets as button tops, and they have worked well for me. I carry a couple lights every day (I have a rotation, so they all get used), and actually USE them at least 20-45 minutes per day. They get knocked around all day on my belt, and dropped very occasionally while in use. Not once has a magnet budged from where I put it.

If the possibility bothers you, then just buy button tops to begin with (I generally do just that...but I try to match the best cells for a given light, and not every cell has an option of button tops, so I do have a few flat top 18650s). In my opinion, magnets are a workable solution...WAY down on the list of things you need to worry about.

Click to expand...

Do you "have" to remove the magnets to charge, or can you leave them in place? The only time I see the magnets having a chance to short things out is during removal. I will be using/ordered rare earth n52 rated 5mm x 2mm magnets. The charger is a Nitecore D4.

Thanks

Hello 009L,

Welcome to CPF.

I remove the magnets when charging with the attitude that it is one less thing that can go wrong. The charger doesn't care unless there is a lot of resistance in the connection.

Tom