coping with 18650 batteries with and without button tops

Just when I thought I knew enough … I discover why a bicycle headlamp wasn’t working. It was because some 18650 batteries have a button top …

some 18650 Li-ion batteries – one with a tag, two with button tops

The 18650 battery, like many batteries, is named according to its dimensions. It is 18mm by 65mm. Most of the 18650 batteries (that I’ve reclaimed from old laptops) have flat tops. They can be with or without tags. Some have button tops. The batteries are the same size but they vary in how much charge they hold and how many Watts they can deliver. Not surprisingly you need differently spec batteries for a laptop, vape mod, electric car, shaver, power bank, an electric drill, a garden mower and so on.

This is the battery holder for a XANES bicycle headlamp bought from Banggood. If you use flat top 18650 batteries in this holder they will not touch the positive terminal and you might puzzle why it’s not working! Two magnets like these (10mm diameter x 2mm thick countersunk Neodymium magnets) will pack the space and provide a button top if you not have the correct cells.

Here are the magnets held in place by magnetic magic. Super glue was used to fix them more reliably. (The lamp now works – and it is so powerful).

Here are two XANES headlamp battery holders. The second time I bought this I opted for a pair of bundled 18650 batteries with button tops. (On Banggood, the price for the same headlamp with 2 x cells and a zip case was £2 more. Bought separately you can pay about £4 per cell).

Be wary that some flashlights need these monster Li-ion batteries called 26650. I was thrown by not having one – although a battery sleeve was included to ‘fatten up’ an 18650 battery so I could still use the flashlight. The yellow battery is fatter at 26mm x 65mm and it needed to last longer because the flashlight gave out so much energy.

Incidentally, these small power banks each contain an 18650 battery. It you have an excess of 18650 Li-ion batteries you can buy an inexpensive kit to turn them into a power bank. The solar panel charging one above cost about £3 and it contains five cells. Here’s how I made it.

How does one end up with too many 18650 cells? Laptops often had a rounded bump at the hinge that contained 4 or 6 x 18650 batteries with a tiny battery management board. When they fail to work for a laptop, I cut these open to find functioning Li-ions cells inside. (Sometimes the laptop battery fails because of the battery management board, but the cells are good).

Did you know that the battery on an electric car consists of loads of 18650 cells held in a plastic matrix? The cells can be recycled as batteries for domestic solar panels.

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