coping with 18650 batteries with and without button tops

I discover my bicycle headlamp wasn’t working because some 18650 batteries have a button top. Oh my, that was embarrassing to admit

The 18650 ‘battery’, like many batteries, is named according to its dimensions. It is 18mm by 65mm. This battery is properly called a ‘18650 cell’ as the word ‘battery’ implies that it is more than one cell.

Most of the 18650 batteries that I’ve reclaimed from old laptops have flat tops. They can come with or without metal tags (to attach wires). Some have button tops for convenient swapping as we’re all used to doing. The batteries are the same size but they vary in how much charge they hold, how many Watts they can deliver and how suddenly they can do that.

Not surprisingly you need differently specified batteries for a laptop, vape mod, electric car, shaver, power bank, electric drill, a garden mower and so on. And even though they’re mostly called Li-ion cells, those 18650 cells may use different chemical inside to suit the different ways that they are used.

Take care: Li-ion cells may have internal circuits to shut them down if they are overcharged or overheat or draw too much power. Those are called ‘protected’ cells. A cell with a button top might be a protected cell. Other cells may not have this circuit perhaps because the laptop, or the charger for example, has the circuit anyway. These are called ‘unprotected’ cells.

So take care in following my tip to use random cells. It’s rarely a good thing to leave a Li-ion battery of any kind on charge so I never leave my stuff charging or forget about something that’s put on charge.

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.