Lithium batteries? can I use 18650 cells?

[andrewheal]

I want to use old stock yet new laptop batteries -- the industry standard size is 18650 -- whatever that means. There are typically 6 of these cells in each laptop battery, but these cells are configured differently for various other application. I would use several of these batteries, like 50 or so. They each can hold 2000mA at 3.7 volts and I can get them for as little as $1 each.  The problem is they are 3.7 volts. So I would need 4 batteries in series and they would be 14.8 volts and even more than that fully charged. Would that much voltage tear up my 12 volt stuff? Safe charge on these is 4.2 volts and 3.7 is dead as I understand things.

 

[blars]

Lithium Cobalt Cells have an inconvenient voltage for 12v applications. They are also a fire hazard. 18650 is 18mm diameter and 65mm long. They loose capacity in storage. 7 in series can be used for some 24v applications.

Lithium Ferric Phosphate is what I recommend for RV applications. Not as energy dense, but longer life, less hazardous, and the voltage range of 4 cells is a subset of the voltage range of 6 cell Lead-Acid.