Valence battery U-Charge RT Series U27-12XP 12V. They have an internal battery management system (BMS) which records the amount of times each battery has been charged and discharged (cycles) and all of these batteries are showing around 25 cycles out of 4000+ that these batteries are rated to do in a lifetime. This means they have more than 99% of their rated life left in them. The internal BMS also shows how well the individual internal cells are balanced and all of the batteries are balanced to within the manufacturers tolerances. All of this can be demonstrated with the app.
LiFePo4 batteries are very safe (unlike LiPo batteries which shouldn't be confused with these) and these exact batteries are so safe they are used in hospitals in medical equipment as well as in road going vehicles made by mainstream manufacturers. The only things to consider are that the batteries should not be charged below 0c and they need to be charged using chargers with correct Lithium charging profiles or customisable charging profiles. Please see below link to the batteries manual for further reference.