Battery state

[PlainName]

Got a small Nitecore torch which started to spontaneously drain the battery. Not an unusual occurrence - the torch has various mitigations against accidental button pressing which could cause unintentional battery drain. However, I started to find a flat battery more often than expected, and it got to the point where simply recharging the battery would cause the torch to turn on and stay on regardless of button press.

So, of course, I took it apart. In pieces it works fine, so I reassembled and discovered that just tightening up the case would cause a spurious button press. You can see from the photo that the buttons are located on a flex PCB, and that positional tolerance must be quite fine. I am thinking that the cause is the battery swelling, pushing the PCB up against the case thus reducing the clearance and causing a button press.

How would I determine if it is indeed the battery swelling? Is there some test, other than measuring the thickness, that would indicate the state? There are no markings and I don't know the original dimensions, nor the expected capacity.

[Manul]

Is that flex PCB with tactile switches just sitting on the battery? Wow, that is exceptionally bad design.

If case, PCB and buttons did not swell (joke), then it means the battery did. I mean, you could measure the weight of battery, find similar weight battery datasheet, then measure capacity or maybe ESR and approximately determine how good or bad it is. But why do it if it is quite clear already. Needs new battery. Or you could reduce the height of the buttons, but this would be kinda stupid to do and likely a very temporal solution.

[PlainName]

There seems to be a gap under the PCB - it can be pressed and deforms a bit. Might not be the battery, but that's why I ask how to check since it would be a real bummer to source a replacement only to find it was something else...

Wow, that is exceptionally bad design

Mmm. I was a bit surprised that there is no fixed support, given the sensitivity of the buttons to position relative to case. But maybe the LED provides that - it is all one PCB folded, and the LED is rigidly fixed in the lens (or perhaps that's all one piece).

[Koray]

How about putting a spacer around the buttons?
K.

[PlainName]

The actuators cover them completely, so that's not practical. However, it might be possible to put a spacer between PCB and case to depress the entire thing a little. Hmmm. Could be onto something there 

[Gregg]

The mere fact that it is not glued together and can be accessed for repair gives some credibility towards quality.  However it doesn’t appear to be sealed against ingress of dirt, water etc. Maybe some dust or corrosion between the battery and the case has tightened tolerances. Possibly you could grind the case thinner below the battery.

The battery does appear to be less than flat in the photo; but that may be due to the close up lens. If the battery is really starting to swell, it probably is only a matter of a short time before failure and may be cheaper to replace the whole unit than source a new quality battery.

Another solution may be to make a gasket between the two halves. 

[PlainName]

The case is 0.62mm thick (it's a pressed sheet) so no chance of making it thinner enough to have an effect

And it cost me £25 (currently £32) so there's no way I'm going to buy a new one.

https://www.amazon.co.uk/dp/B07GZSF6D8

You can see from the attached image the arrangement of the buttons.

[PlainName]

The battery didn't seem to be touching the PCB, so I tucked the bottom right corner of the PCB into that space a bit better, put it together and it is fine. Hmmm. I can't see this being a permanent fix, but it does indicate that the battery expanding wasn't the cause, which answers my question