The thermal focal lengths, absorption efficiencies, and laser performances of Er:YAG and Er:LuAG crystals are systematically demonstrated within an anti-misalignment double corner-cube-prisms resonator. The maximum continuous-wave output power of 5.12 W at 1645.39 nm and 6.43 W at 1650.33 nm are obtained, with slope efficiencies of 16.29 % and 36.78 %. In pulsed operation, Er:YAG yielded a maximum pulse energy of 5.1 mJ, and Er:LuAG delivered 4.7 mJ, both at the pulse repetition rate of 200 Hz. The beam qualities, represented by M2 factors, are measured at 1.52 for Er:YAG and 1.44 for Er:LuAG.