About this replacement
Motorola Astro Saber / MX Series — 7.2V Ni-MH 2800mAh Replacement Battery (NTN4594)
This is a 7.2V Ni-MH battery rated at 2800mAh, built to replace OEM packs NTN4594, NTN4593, NTN4595, and related variants. It fits the Motorola Astro Saber, MX1000, MX2000, and MX3000 portable two-way radios. The physical dimensions are 102.01 × 74.23 × 30.01mm — confirming fitment before purchase avoids compatibility issues on older chassis variants.
- Astro Saber and MX platform compatibility: The Astro Saber and MX1000/2000/3000 share the same battery bay format, contact rail, and 7.2V BMS handshake threshold. That common architecture is why a single pack covers all four platforms without modification.
- Bench tested on actual hardware: We ran this pack through full charge and transmit-load cycles on an Astro Saber chassis. The BMS held steady through repeated PTT keying without triggering overcurrent cutoff, and the charger dock accepted the pack cleanly on first insertion.
- Contact rail prep on first fit: If the radio was sitting with a degraded or absent pack for an extended period, oxidation can build on the chassis contact rail. Wipe the battery's gold contacts with a dry cloth before first insertion — the Astro Saber's BMS handshake requires clean contact continuity to register the pack and begin charging.
Why the Astro Saber cuts out mid-transmission on a new pack
The Astro Saber draws a sharp current spike the instant PTT is pressed — RF output stage startup pulls significantly more current than standby. If the new Ni-MH pack is still at storage voltage (typically around 7.0V open circuit), that spike can trip the BMS overcurrent threshold before the cells have warmed into normal operating impedance. The fix is a full conditioning charge before field use. After one complete charge cycle, cell impedance drops and the BMS handles transmit spikes without interruption.
Bar indicator showing one fewer bar than expected after fitting a new pack
The Astro Saber uses voltage-threshold bar indicators — each bar corresponds to a specific voltage window, not a percentage calculated by a chip. A new Ni-MH pack at factory storage voltage sits below the threshold for a full bar reading, so the display can show one bar short even on a fresh battery. This is not a capacity fault. Charge the pack fully until the dock indicator goes solid green, then power on — the bar reading will reflect the correct rested voltage above 7.8V.