We had 1°F here this morning. The lithium ion cells with the 'button' are often protection type cells while the 'flat' top are not. That is they have a tiny board inside that protects them from overvoltage and overcurrent. The 650 in 18650 (like all lithium based cells) refers to the physical size. 18mm diameter (although they are typically a little wider with their wrapping, and 65.0mm long. The protected type are longer, about 68mm. Soldering to the protected type will frequently destroy the protection board. The very common 2032 coil cell for example is 20mm across and 3.2mm thick. Lithium Iron Phosphate is a better choice for direct replacement of lead-acid because the cell voltage makes better matches to common lead-acid.
I may be behind with this comment. Really like the new look!
We had 1°F here this morning.
The lithium ion cells with the 'button' are often protection type cells while the 'flat' top are not. That is they have a tiny board inside that protects them from overvoltage and overcurrent. The 650 in 18650 (like all lithium based cells) refers to the physical size. 18mm diameter (although they are typically a little wider with their wrapping, and 65.0mm long. The protected type are longer, about 68mm. Soldering to the protected type will frequently destroy the protection board. The very common 2032 coil cell for example is 20mm across and 3.2mm thick. Lithium Iron Phosphate is a better choice for direct replacement of lead-acid because the cell voltage makes better matches to common lead-acid.
Thanks for the info.