PCB Protected 18650 Battery

SAFETY FIRST. When you buy most 18650 batteries they DO NOT come with a built-in overcharge/discharge protection system. Commercially made devices (hopefully) incorporate this circuitry elsewhere, but for applications such as building a Meshtastic radio nodes from scratch, you have to DIY.

This Instructable is a follow-up to my Meshtastic Solar Buoy project published in April 2025. If you choose to re-use the stock 800 mAh battery from your Solar Buoy, I highly recommend the "In-Line" style chips sold by PeakMesh on Etsy for minimal fuss. Once I receive mine in the mail I will update this post with pictures of those. Other styles of PCBs are designed to connect directly to your battery and are barely noticeable once shrink wrapped.

I've included #affiliatelinks in the Supplies section so you can click and help me fund more how-to Meshtastic Instructables!

1) One "flat top" 18650 lithium-ion battery cell of your choosing. Rokland | Amazon

2) One battery protection PCB chip. Linear Style | Button Style | In-Line Style (PeakMesh)

3) One 2.0mm JS style battery connector. Amazon | Rokland

4) 18650 Battery Insulation Discs. Solid style, not "hollow". Amazon

5) 21700 Battery Shrink Wrap (oversized to accommodate the PCB). eBay | Amazon

6) Wire cutter/stripper. Amazon

7) A hair dryer or heat gun to shrink the wrap. Amazon

8) Solder and soldering iron. Amazon

9) Battery spot welding tool (optional). Amazon

10) Battery load tester (optional). Amazon

1. If you order a fresh 18650 from Amazon or Rokland you should be in good shape! If you need help selecting an alternative, the Oscar Liang website has done a ton of field testing: https://oscarliang.com/best-18650-li-ion-battery/

1. If you are recycling an 18650 from an old power tool or other gadget, be sure to load test the cell first to make sure it can hold a charge. I got excited once when I received a "refurbished" Ryobi 18 volt battery pack that would no longer charge. I hoped perhaps just the charging circuit had gone bad and I could salvage the individual cells. In reality only two of the ten cells were usable I wasted a lot of time on the effort. Rule of thumb: If you measure the voltage and it's below 2.5 volts (even if the cell hasn't been charged in a long time), the cell is likely damaged.

1. If you are re-using the 800mAh battery that comes with a Solar Buoy, I highly recommend using the plug-and-play In-Line style chip sold by PeakMesh on Etsy. Alternatively you will need to:

1) Remove the outer shrink-wrap

2) Remove the paper insulation discs from the positive and negative terminals

3) Pry off the spot-welded battery tabs to get down the the bare cell. Use a sturdy pair of pliers, grad a tab and twist to roll it up onto itself and around the pliers. It should come off fairly cleanly and not damage the cell.

1. Use wire cutters to snip one chip off from the panel/array. The board is marked with white lines on each end for where to cut.
2. Inspect the ends of the PCB and your cell to match polarizations. Make sure the end marked "B+" on your PCB will be connected to the positive terminal of your 18650. The positive terminal is generally the smaller metallic circle surrounded by a white plastic ring.
3. Inspect the the center of the PCB and find the "P+" and "P-" solder pads. These are where you will solder on your JS style power connector. Make sure the polarity of your wires matches the pads when you solder.
4. Solder your JS connector leads to the solder pads. I like to make sure both wires are angled up towards the positive terminal.
5. Solder or spot-weld the negative and positive terminal strips from the PCB to their respective battery terminals.

1. Use wire cutters to snip one button chip off from the panel/array.
2. Inspect the circuit board side of your chip and observe that there are two terminal strips of different lengths. The short strip connects to your negative terminal, the long strip to positive.
3. Inspect the plastic cap that comes with the button. One hole is closer to the edge and cuts into the outer rim. This is the hole for your positive terminal strip. The other hole is more inward from the edge and does not cut into the outer rim. This is for the negative terminal strip.
4. Fold both terminal strips upward so that the solid silver disc on the underside of the chip is pointing the opposite direction of the strips.
5. Insert the long positive terminal strip through the cap hole that cuts into the outer rim.
6. Insert the shorter negative terminal strip through the other hole.

Attaching the button style PCB is a bit more complicated than the linear style.

1) Fold the shorter negative terminal strip up and across the plastic cap. I like to use a small flat object to crease the strip so that it folds at the outer edge of the plastic cap. This ensures the strip will not touch and short circuit the positive strip when it is attached to the battery.

2) Unfold the creased negative terminal strip and solder or spot-weld it to the battery's negative terminal. Make sure it is oriented so the face of the plastic cap is facing towards the battery.

3) At this point you should have a little sandwich: Battery | Short terminal strip | Plastic cap | PCB board with the metal PCB board base facing away from the battery.

4) Solder your negative JS connector wire to the metal disc exposed by the PCB board.

5) Cut the length of your positive JS connector wire by about one battery length so your wires will end up nice and even at your connector. Strip and tin about 3/8 inch of the newly cut positive connector wire.

6) Solder the positive JS connector wire to the battery's positive terminal.

6b) Alternatively you can solder small terminal strip tabs of metal to the positive and negative connector wires and spot-weld those tabs to the PCB and positive terminals.

1) Insert your battery with PCB and attached connector into a 21700 battery sized sleeve of shrink wrap. Keep it centered along the length of the sleeve.

I don't know why all these kits you buy on Amazon come with "18650" sized shrink sleeves. Unless you are planning to strip your cell down to bare metal on all sides these sleeves will not fit over the stock shrink wrap already on the cell! The 21700 size is a little harder to search for, but it fits and shrinks with ease.

2) Add a SOLID style insulation disc inside the sleeve on each end of the battery.

Again, I don't know why all these kits on Amazon come with "hollow" style discs with a hole punched in the center. You can leave the hole punched piece in place, I've done it, but if it that center ever falls out you again have an exposed terminal. The "solid" style discs eliminate that risk.

This is the final and most fun part!

Use a hot hair dryer or heat gun to shrink the shrink wrap.

1) Start shrinking at the end with protruding connector wires to make sure everything is seated properly.

2) Next shrink the bottom to make sure the sleeve wraps around the bottom of the cell and doesn't come up short.

3) Finally shrink the middle and rotate the battery around to make sure everything is nice and tight.