Tutorial: Rewrapping a battery

Rewrapping a battery

The above battery cannot be used anymore, it will short and might explode.
The wrapping will sometimes break, luckily it is a fairly simple operation to fix it.

Tools and parts needed

I am using shrink wrap to repair the battery, due to the heat gun I uses, I have selected a low temperature type.
When flat it is 29.5 mm wide, the inner diameter is 18.5 mm, it will shrink at 80 Deg. C.
I bought a roll with 25 feet (7.6 meter) on ebay for $11 (Sellers name is atop_authentic_auction). This roll will last for more than 80 batteries. Fasttech has heat shrink in 1 meter pieces for less than $1.
This heatshrink is also fairly thin, this is an advantage for some lights.
Often heat shrink is specified in width of the flat tube, the table below shows the minimum sizes for different battery sizes.

As a heat gun I uses a hair dryer, it is not the perfect tool for the job, but it can be used.

I do also need something to measure with, my digital caliper is fine for that (A ordinary ruler could also be used).
With a caliper, remember to cover the jaws or it will short the battery.

To cut the heat shrink I uses scissors.


I want the heat shrink tube to be about 3 mm longer than the battery at both ends, with a 68 mm battery this means 74 mm tube.

The new tube for the battery has been cut of the roll.

I uses the fingers to removing the old heat shrink, using a knife or scissors is unsafe.
If there is two layers of heat shrink, only remove the outer layer.

The "naked" battery, do not try to bend the protection pcb out to get a look.

Putting the new heat shrink onto the battery.

There will be about 3 mm extra at each end.

Applying heat, rotate the battery and swipe the heat gun back and forth. If using a real heat gun, be careful with the fingers holding the battery!
It is possible to increase the temperature by covering part of the air intake on the heat gun (This might also melt the gun if overdone).
The battery must not be heated much (As long as it is possible to hold it, the temperature is fine). This is usual not a problem, the heat shrink will shrink long time before the battery is heated.

Final result

With a new covering, the capacity information is gone, to fix that I have added a label with capacity. I also included the date I got the battery.

Awesome tutorial, thank you very much!

I would just like to add that a very similar or even the same wrap used by HKJ is avaliable at FastTech at 1m units:

Thanks for posting this HJK. One of my Trustfire 26650 5000mAh cells is starting to loose part of the wrapping. I’ll order this shrink wrap and make the fix.

Also glad to see I’m not the only one that uses labels to print the purchase date on the cell :wink:

I’m not quite sure if the shrink wrap will be able to wrap a 26650 cell, might be too wide… 0:)

Thanks for the heads up. I’ll take some measurements of my cell and find the correct diameter for a 26650.

No problem, I’m sure you’d figure it out sooner or later. :stuck_out_tongue:

Thanks for the great write-up!

It is not exactly the same, the one I uses is without glue.

You have to get something that is slightly above 26 mm in diameter

My experience with pens is that the markings does not last, with these labels it will last.

Thanks for pointing that out.

Do you know how different it will be with the adhesive?

I use an industrial Sharpie for all my cell writing, haven’t had issues with it yet…

I have not tried with adhesive, but I will not expect any different when rewrapping, the final result will probably be a bit stronger.

I have ordered this shrink and it is without adhesive glue whatever…just blue plastic which is a tight fight on a 18650.

pictures in another thread:

I also rewraped a 16340 with the fasttech shrink, this worked but the wrap doesn’t get perfect plain…

Thanks for the confirmation!

Nothing but red x’s…can’t see the pics.

Looks like the server is down, it will probably not take very long before it is up again (I uses a hosting service).

Cannot see pics at the moment.

They are back again.

Nice, thanks!
I have re-wrapped some batteries, did not bother to measure the wrapper before cutting. Just estimated it by eye.

I think after re-wrapping it feels at least as much if not more durable than before.

HKJ gives good advice.

I use a Laundry Marking pen from the Office Supply to mark cells. This is better than the so called “permanent marker”. The Laundry Markers are the ones that never wash out of clothes, even in hot water. Don’t get it too oily before you mark it.

If you mark it….better check your spelling first, you ain’t gonna change it.

Thanks for the tutorial