protection circuit Lithium-ion batteries
A1.  The built-in protection for li-ion cells should be considered "emergency protection"--it should not be relied upon for normal cycle V &amp; A protection. In a "safe" battery design, V&amp;A protection should "always" be included in your design.

A2.  A thermistor protected battery system is wise.  Sometimes li-ion cells do not dis/charge at the same rate &amp; cause an imbalance in the series/parallel configuration of larger Ah batteries.  A thermistor can be used to detect an overheating condition, prevent a fire, slow the dis/charge rate/s, or indicate a dis/charging fault in a smart battery system.  I consider it very important in a safe battery system, but, it is often overlooked or ignored when ICR type li-ion cells are used. If you want to make a safe battery pack, then I suggest you always include a thermistor &amp; supporting circuitry--don't allow the incomplete/shoddy designs of others to affect your design decisions.