All Motorola MOTOTRBO batteries are IMPRES meaning they automatically recondition themselves depending on individual usage patterns. All are rugged, carry the IP57 submersible rating, and have an 18 month warranty.
The MOTOTRBO XPR6100, XPR6300 and XPR6500 series have a choice of four different types. For longer use between charges the best choice is the high capacity PMNN4077B. It provides 47% more capacity and is also Li-ion so it will not develop memory effects. When budgets are tight the PMNN4065A does a good job too.
If your XPR radios have the intrinsically-safe option for use in hazardous atmospheres choose the PMNN4069A FM rated battery. Both your radio and battery will have a green dot on the bottom if they have this option.