Noob battery question re flat vs button top

Revlio · 2019-01-09T19:30:17.000Z

How do I tell if a flashlight needs a button top 18650 or flat top? Also, will the light not work with the wrong one? Not being an EE major, I’m thinking wouldn’t the spring cover the small difference in size or just be pushed in a little more? I ordered a Emisar D4 and some flat top batteries and am wondering… Thanks guys.

ChrisGarrett · 2019-01-09T19:57:56.000Z

Most flashlights have a spring at the rear of the light for the negative end of the battery/cell. Some also have a spring at the positive end, near the head of the light. Still, some lights have what’s called a ‘reverse polarity protection’ setup up that will not allow flat top cells to make the negative (on the battery/cell) connection when placed inside the light backwards, due to some raised protrusions on either side of the positive pad. This keeps the flat top cell from damaging the light.

If your light has springs at both the positive end and the negative end of the light, you can use flat top cells, which is how the manufacturers (Sony, Panasonic, LG, Samsung and Sanyo ship them from their factories) make them.

If you need a button top battery because you have a light that has no forward spring and does have the RPP setup, you can find 3rd party vendors adding button tops to the above cells for a buck, or two, more.

Your Emisar D4 has spring contacts at both ends and will accept flat top cells.

Look to the Sony VTC 5a high current cells for your D4. I have both the D4 and the D1S.

Chris

Klotski · 2019-01-09T19:52:54.000Z

Revlio
I personally use the search function to check and see what the reviewers have to say. Most of the lights have been reviewed and some more then once and they will usually tell us what works or doesn’t? probably doesn’t help you right now but the reviews published here are very good and will answer a lot of questions.
Paul

Revlio · 2019-01-09T20:11:34.000Z

Thanks guys. I have been reading reviews but also noticed its not often mentioned there or one the seller’s pages. Have a good one.

sbslider · 2019-01-09T20:17:00.000Z

So you got information as to why flat top cells will work in your D4, as it has springs for both contacts. Springs would also accept button top cells.

At the risk of putting my foot in my mouth, I’ll say all 18650 cells start as flat top and bottom. Simpler to build in large quantities I believe.

So why button top cells then? Well, to reduce the size of a light you can remove one spring and have the cell contact directly to a PCB. Lots of common cells work great with this (AA, AAA, C, D, etc). 18650 cells have an exposed contact, but also have a plastic sleeve around that contact, may not work so well when trying to make a connection to a flat PCB. If one adds a small protrusion (button) to the top of the cell, now it contacts a circuit on the PCB easily without the plastic sleeve interfering.

Simple as that for most situations. One other minor plus for button top cells as it makes identifying the polarity of the cell (which end is “+”) a bit easier.

BTW, I noticed you are interested in the BLF lantern, that light is designed for button top cells. Don’t rush out and buy cells today, as the light won’t be available for at least a couple more months I suspect.