18650 Battery Magnetic Charge Holder

I need low power magnetic holder which is simple and quick to connect and disconnect. At the same time, has a releable connection. Here is my solution. I prefered it to real heavy duty 18650 battery holders which are realy pain with battery insertion and extraction. I use my design when I need to charge some cells to storage voltage (3,8V) or need something to power with a single lithium-ion cell. I have several different brand chargers like SkyRC MC3000, but this magnet holder does bit all of them in connection simplicity and speed. 

As I always use to mention: 

be careful with this type of batteries, which can store lot of energy. You can hurt yourself seriously and you can burn down your home, if you do not know what you are doing. You yourself are responsible for what you are doing with this information.

Never: 

• make a short circuit on a battery!
• charge a single cell with a voltage greater than 4.2V DC!
• miss battery and connection polarity!
• over discharge, which is only dangerous for battery life and capacity.

Material used: 

• neodymium round magnets dia 9 x 4mm, 2 pcs. Can be obtained from Aliexpress, Amazon, Ebay. I have used ordinary whiteboard pin magnets, where I picked up the magnet from the plastic pin. Pin magnet diameter is aprox. 12 x 21mm. Magnets 8 x 4 may be used, but you need to make outer shim as well as 8 x 3mm with addition of a suitable washer.
• Nickel strip which is used for welding on battery contacts. Dimmensions are shown on provided pictures. External wire will be soldered to one end.
• if you do not have nickel strips, you can use tinned copper wire. I do not suggest to use bare copper wire. The wire has to be tinned. 0.1 to 0.2 mm in diameter would be fine. You can find these wire in a stranded connection wires  and in shielded cables. Wind it round the magnet and holder as my pictures show.
• AWG24 (0,25mm2), red for “+” pole, and black for “-” pole. I use PTFE (teflon) insulated wire, with very thin insulation. Both versions of battery magnetic holders have a side hole for wires. These holes need to be cleared with 1.5mm bore prior to use. If you have AWG24 wire with thick insulation or if you use AWG20 (0.5 mm2), you can pull wire through cap hole instead.

For one battery connection you need to print: 

• 2 pcs of Battery Magnetic Strip Holders or 2 pcs of 18650 Battery Magnetic Wire Holders.
• two caps
• one Plus sign for “+” pole.  Has to be of red colour.

Marking: 

When all parts are printed, magnets and contacts installed and wires soldered, 

• red wire and a cap with red  “+” sign for PLUS terminal. Both caps are identical, but you can print just one cap in red colour for plus terminal only.
• black wire and a cap without any additional sign. There is a groove “-” shaped on the top, which indicates that it is the MINUS terminal.

How to use magnetic holders?

• make your own lithium-ion battery charger. Buy som  TP4056  lithium battery charger module and solder wires on the output of this board. Power it from PC's USB connector.
• Charge your batteries from a lab power supply. Use this method ONLY if you know what you are doing. I used this method to simply charge some cells to Storage Voltage of 3.8V, where current is limited to 0.5A in CC mode (constant current). How I made my own Power Supply, can be found here.

These holders does fit very nicely on a AA primary or NiMH batteries too. 

You will notice how quick it is to connect or disconnect a battery. 

The top cap holes may be used (if they are free) for voltage check, with multmeter probes.