Protection end caps increase length and generally don't fit the robots. Protection PCB boards were used. Also the specific brand of the LiFePo4 project is advised. Major suppliers A123 etc. known in the industry, for cars and solar power etc., electric bikes.
Check details of balancer boards in the project as only certain ones can activate the thermistors with enough heat, and whether protection is used. There is a wide range of battery characteristics supplied in different cells for different applications, and only certain ones match robot requirements. DIY batteries are experimental, no guarantees. Much more has been done on XV models with software settings for lithium charging (not for LiFePo4, different voltages).
LIFePo4 is inherently safe like NiMh and protection is for the battery damage only, no fire hazard like lithium ion. Soldering is possible with a high power iron or gun used quickly not to damage the battery, no fire hazard. If interested, the Lithium Ion Revisited thread shows possible circuits for simulating thermistor control signals instead of actual heat transfer from balancing boards. 74665 voltage comparator. XV lithium ion replacements for NiMh have proprietary circuit boards of this kind, with microcontrollers, very thorough. LithiumPower/AnewPow also supplies a Botvac
 Carefull assembling packs not to short out a battery with stray wiring; use tape on all loose wires etc. during assembly. Cells support high currents, dangerous sparks and heating, like car batteries.