proper and safe way to measure battery length

boo · Jun 14, 2016

I have been using 18650 li-ion batteries of late.
Noticed that some batteries are shorter than some
others I have on hand.
My first thought was to use a dial caliper to measure
them.
Then it dawned on me that by touching the top and
bottom of the battery with the same instrument, it
might short my battery.

How do others here safely measure a batteries length?.
Thanks boo

Ladd · Jun 14, 2016

I have often wondered if anyone used a caliper to measure a battery and if they lived to tell the story. Would make a good video :poof:

I just use a plastic ruler along the side of the battery. Close enough for Govt. work.

Or, could cover the battery terminals with Kapton tape?

boo · Jun 14, 2016

Ladd said:
I have often wondered if anyone used a caliper to measure a battery and if they lived to tell the story. Would make a good video

I just use a plastic ruler along the side of the battery. Close enough for Govt. work.

Or, could cover the battery terminals with Kapton tape?

Your post made a light go off in my head. When you mentioned "plastic",
I remembered that my dial caliber is made of hard plastic.
Should be ok to use it, right?.

Lynx_Arc · Jun 14, 2016

boo said:
Your post made a light go off in my head. When you mentioned "plastic",
I remembered that my dial caliber is made of hard plastic.
Should be ok to use it, right?.

Yes. You could also just use scotch tape or a piece of paper on both ends for the purpose of fitting the small additional length added by it would help for a margin or error.

staticx57 · Jun 14, 2016

$7 on one of the Chinese sites

ShineOnYouCrazyDiamond · Jun 14, 2016

Just use electrical tape on each end of the caliper where the battery would contact. Then push together and re-zero the readout.

ChrisGarrett · Jun 15, 2016

ShineOnYouCrazyDiamond said:
Just use electrical tape on each end of the caliper where the battery would contact. Then push together and re-zero the readout.

Yep, absent any plastic calipers, I'd just put a piece of Scotch tape on the jaws and rezero.

I've yet to bother, but I have a nice Mitutoyo set. My beater set is a Midway China special, but it works pretty well after 20 years.

Chris

Timothybil · Jun 15, 2016

staticx57 said:
$7 on one of the Chinese sites

I have that one as well, and it works fine for me. I have used it a few times to measure cells. Most recently I used it to try to figure out what size magnets to put on some unprotected cells so I could use them in my Nitecore lights.

boo · Jun 16, 2016

Hate to switch subjects in the middle of a thread but, many people mention using magnets
on top of their batteries to extend the length of the battery.
What kinds of magnets are these and where can they be bought?.
Why a magnet instead of just using some type of metal like, copper
for instance?.

ChrisGarrett · Jun 16, 2016

boo said:
Hate to switch subjects in the middle of a thread but, many people mention using magnets
on top of their batteries to extend the length of the battery.
What kinds of magnets are these and where can they be bought?.
Why a magnet instead of just using some type of metal like, copper
for instance?.

What happens if the conductive disk shifts and creates a short with in the light...say if you drop the light?

Ka-boom!

Cleanup on aisle 7 please, may I get a mop bucket on aisle 7?

Magnets are better, those rare earth neodymium ones that are strong, but they create their own resistance and that might be problematic.

Best practice is to just use a cell that fits as is, whether it's protected, or not.

Chris

Crazyeddiethefirst · Jun 16, 2016

Well heck howdy, I just measure the distance on the battery with a piece of string and then put that length of string against a ruler....
Of course, when my indoor furniture gets too worn out it becomes my patio furniture too...

archimedes · Jun 16, 2016

I do wish that the potential risks of "magnets" were more clear to any who may be less experienced readers of this forum ...

fivemega · Jun 16, 2016

boo said:
Why a magnet instead of just using some type of metal like, copper
for instance?.

Magnet most likely (not always) stick in middle of battery terminal but copper metal will move around and make short circuit with metal barrel of flashlight.
So, magnet is safer than bare metal but not 100% safe.
When it comes to magnet size (for example) 4mm D and 2mm L, total resistance of copper, earth magnet and aluminum is almost same and not noticeable.

TinderBox (UK) · Jun 16, 2016

Anybody tried a drop of superglue around the magnet to stop it moving.

John

m4a1usr · Jun 16, 2016

You know I keep reading these stories here on CPF over the years (magnets to extend connection in a short OAL) and it makes me wonder why one of us hasn't just took a 18/17/16mm delrin rod and bore it to accept a 1/4" brass dowel, press in the brass conductor and cut them to some standard (that might have to be defined?) length? That would keep the conductor placed where it needs to be and the delrin providing insulation to the host body. You could drop your light all day long and never have to worry about a magnet moving. They might even catch on?

ChrisGarrett · Jun 16, 2016

m4a1usr said:
You know I keep reading these stories here on CPF over the years (magnets to extend connection in a short OAL) and it makes me wonder why one of us hasn't just took a 18/17/16mm delrin rod and bore it to accept a 1/4" brass dowel, press in the brass conductor and cut them to some standard (that might have to be defined?) length? That would keep the conductor placed where it needs to be and the delrin providing insulation to the host body. You could drop your light all day long and never have to worry about a magnet moving. They might even catch on?

They have and there are pics.

Thin fiber washer, sanded down to make it even thinner and then a brass rivet inserted in the center, pounded flat and filed down to fit.

A member posted one here for flat top batteries not making contact with the reverse polarity protection 'protrusions' found on many drivers.

The diameter of the fiber washer is made to fit inside the light's tube, but not so much that it's able to shift around and break contact, or cause a short.

Chris

archimedes · Jun 16, 2016

m4a1usr said:
You know I keep reading these stories here on CPF over the years (magnets to extend connection in a short OAL) and it makes me wonder why one of us hasn't just took a 18/17/16mm delrin rod and bore it to accept a 1/4" brass dowel, press in the brass conductor and cut them to some standard (that might have to be defined?) length? That would keep the conductor placed where it needs to be and the delrin providing insulation to the host body. You could drop your light all day long and never have to worry about a magnet moving. They might even catch on?

Yes, I have a bunch of these ... all made by several different CPF'rs

Overclocker · Jun 17, 2016

got this from harbor freight

TinderBox (UK) · Jun 17, 2016

I have an Mitutoyo Vernier i bought for £80 years ago, but an fiberglass/plastic would be handy so i just ordered one from an eBay UK seller for £3.99/$5.70 free 1st class delivery, could have ordered from China £3.29 the difference is not worth the long wait.

John

Timothybil said:
I have that one as well, and it works fine for me. I have used it a few times to measure cells. Most recently I used it to try to figure out what size magnets to put on some unprotected cells so I could use them in my Nitecore lights.

kosPap · Jun 17, 2016

m4a1usr said:
You know I keep reading these stories here on CPF over the years (magnets to extend connection in a short OAL) and it makes me wonder why one of us hasn't just took a 18/17/16mm delrin rod and bore it to accept a 1/4" brass dowel, press in the brass conductor and cut them to some standard (that might have to be defined?) length? That would keep the conductor placed where it needs to be and the delrin providing insulation to the host body. You could drop your light all day long and never have to worry about a magnet moving. They might even catch on?

I have made several kinds of spacers in the past, and one can search for them. but this is my lattest version and the easiest to do
(faucet rubber washers and a brass spring extension from switches in several chinese lights like the C8)

proper and safe way to measure battery length

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