Thrunite 5000mah protected(?) 26650 unwrapped

Ive been confused by Thrunite’s 5000mah 26650 since it came included in my catapult pro.

It says protected, but there’s no nickel strip or circuit board I can see or feel, it’s not protected in the usual way.

The negative terminal has “thrunite” etched on it, which is cool, but seems like a safety issue if that’s on the actual steel can. But thrunite assured me it’s not. So it must be the bottom of the PCB then, obviously. I can’t see or feel anything there though. A PCB is really obvious attached to a battery. Doesn’t make sense.

But it shows ~300mohm internal resistance so its definitely a protected battery. Somehow.

My 26650 sizes wrap came in, to rewrap it afterwards, so finally decided to check it out.

So huh. Never seen anything like this. I guess they must have some kind of protection built into the top of the cell, maybe a beefed up PTC and there’s what looks like some mesh, I guess maybe to catch pieces of battery that would fly out while venting? Idk, I’m not taking that apart any further right now.

That’s all fine and dandy, but why the piece of tin tacked on to the bottom? Im not even sure it’s spot welded, just has 4 little pointy feet. If it’s a spot weld it’s the weakest spot weld I’ve ever seen.

What’s the point of this? Just so they could write thrunite on the thing? To add a ton of resistance and “protect” you from having a bright flashlight? Or maybe to protect the actual can from being damaged by the sharp double springs on the tailcap you can’t access.

Whatever the reason, it’s dumb and so are protected batteries.

My TC20 PRO came with the same cell. It’s a full 70mm long…too long. Overcompresses the tail springs (double as well in this model). I’m shopping for an unprotected replacement, but it’s tough to find a quality 26650. I’m kinda leery of the Vapcell K62 after all the kerfuffle over excessive self discharge. Everything else is out of stock in all the reputable suppliers in the U.S., and NWIH am I buying cells off Aliex.

Thank you for taking one for the team.

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The protection circuit is in the metal section above the green wrapper. That whole silver piece is tacked on top off the unprotected cell.

This was exactly the same as a ThruNite 18650 that I purchased years ago. It was a Panasonic NCR18650B with the protection circuit on top.

The question is how does it work? Normally, as mentioned, there is a metal strip running from top to bottom. The circuit knows what the cell voltage is as a result of this strip. So with overcharging (V > 4.20V), and over discharging (V < 2.5V), the protection kicks in.
There is no strip, so the circuit is as far as I know only able to measure current. So the protection is only able to kick in when a certain current value is reached.
So the “protection” should be very limited compared to conventional protected cells. At least this is how I perceive the situation.

There’s no need for a metal strip. The top of the can has both the positive and negative easily accessible (for the protection PCB).

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Its definitely possible. Do you have any pictures?

Ive seen ones where the circuit is inside a plastic tab that just looks stuck on to the top of a finished battery. They couldve done that here and then enclosed the whole thing in that steel top, stamped it down and spot welded it shut.

I can’t find any pictures of that steel cap pried open. Sooner or later I’ll get curious or bored and totally destroy the battery to find out.

But I’m going to get some actual use out of it first, because the ‘internal’ resistance is now a usable ~30mohm. Just by taking that dumb thrunite plate off. I’m almost certain the purpose of that was abrasion resistance from the springs. They should have just made it out of a more conductive metal and in better contact with the rest of the can so it didn’t add so damn much resistance.

Sorry, I didn’t take any pictures when I ripped it apart. I only disassembled it because the battery went to zero (and was still close to zero after removing the protection). The battery has long been recycled.

Aha! Yes I understand now.

Whats it look like underneath? Just a normal 26650?

Mine was a Thrunite 18650, but yes, it was just a regular Panasonic NCR18650B (green wrapper) once I ripped off white Thrunite wrapper. I then ripped off the top silver can, the protection PCB thingy and what was left was just a regular unprotected cell.

I’m not 100% sure it’s the same thing. On the thrunite website on the page for the 18650 they advertise that a protection circuit has been added on to the top.

“Add metal cover on the positive end. Avoid short circuit risk from shrink wrap damage.” is their exact quote. They have a little Photoshop rendering of what that looks like.

Theres none of that on the page for the 26650…They have a few different kinds of batteries on the website. Ones that look like they have regular protection circuits, an olight style one with that weird plastic ring on the positive cap, one that they call protected but say is compatible with any flashlight and has a length of 64.5mm.

But they also state the standard charge current for the 26650 is 25amps, so maybe none of that means anything.