On 11/15/2017 7:56 PM, Jeff Liebermann wrote:

Or you can get the ones not specified as battery extenders
https://www.ebay.com/itm/N35Super-Strong-Round-Disc-10x1mm-10x2mm-Magnets-Rare-Earth-Neodymium-N35/361874792648
for 3-cents each in hundreds.

Nice price. However, 10mm wide is MUCH too large for a button top
replacement. The eBay offering did not mention the size, but
measuring the one's I'm using produced:
6mm diameter x 0.84 mm thick.

Measuring the normal size of the stock button top on a typical 18650
cell, I get:
6mm diameter at the base x 2.5 mm thick.

click the size selector on that page.