Modifying Flat-Topped Li-ion Cells to Fit Into Battery Holders




About: Autistic person who's interests include utility cycling, recreational cycling, cycling safety, electronics, gardening, Arduino, and LEDs.

Many 18650 cells have surfaces on both sides, making it suitable for solder tabs but they might not fit into certain battery compartments such as those found in flashlights. To modify the flat top, simply melt a blob of solder onto the positive terminal. Do it quickly as you want to heat only the terminal.

Another bonus of this trick is that it makes it easier to identify the polarity in the dark.



    • Trash to Treasure

      Trash to Treasure
    • Paper Contest

      Paper Contest
    • Pie Contest

      Pie Contest

    8 Discussions


    6 years ago on Introduction

    Solder (tin?) is a bad option for contacts. You could use a little brass wafer soldered over the tip of the battery. It is not optimus, but is far better than only tin.
    I say this by experience.

    7 replies

    Reply 6 years ago on Introduction

    Not only more conductive, tin oxidize easily and lose contact. Brass is better than both.


    Reply 6 years ago on Introduction

    rimar2000 is in "one of those" places in the world. :-)

    Copper would make a better conductor, and sheet(or round slug bits) copper should be around the same price as brass anyhow.

    MY personal favorite, is to get a 5mm neodymium magnet and stick it on the end.
    As long as you're not building a battery pack, the metallic plating on the magnet should be more than conductive enough. To illustrate how well it works, I once did a series of tiny spot welds, using 6x18650, 4 harddrive magnets(one whole, and 3 broken in half) , and a stainless steel paperclip. the 5mm round X 2mm thick magnets are usually more than enough to fix any contact gaps.


    Reply 6 years ago on Introduction

    Exactly right, with the solder.

    A person CAN solder onto those contacts, but it's VERY tricky.

    IF you're going to try this... practice on dead cells first.
    TOTALLY dead cells. Then let the dead cells sit around a few months just to make sure. the low voltage cutouts in an 18650 can leave a charge inside the battery for a LONG time, even though a volt-ohm meter reads "zero volts" at the terminals.
    Finally, rough up the contact a little with some fine grit sandpaper, emery cloth, or a dremel grinding wheel.
    When soldering, use good acid activated flux and a nice medium or large HOT iron.
    The flux will help remove the nickle-oxide layer, to help the solder bond... and the larger hot iron will allow you to get the heat on and then back off the surface of the cap much quicker, which should minimize the chance of breaking your battery.