For general use, Alkaline AAA batteries are the most cost effective and provide good battery life. Lithium AAA batteries offer the best performance in cold weather, are the lightest, and last the longest but cost significantly more. Rechargeable batteries such as NiCad or NiMH should not be used as they do not provide sufficient and consistent voltage to operate the receiver effectively. Always use name brand batteries like Energizer or Duracell with a comprehensive warranty. Three red LEDs illuminate the entire control panel for better clarity in the dark without compromising your night vision. The most sensitive UHF telemetry receiver available, providing the best tracking range possible. Compact and rugged one piece design allows quick deployment and maximum portability in the field Applicable models are FM500 434 and FM2000 (433 & 434)