First Officer reported a power brake failure on approach to landing. Knowing that the normal brake system and auto brakes/anti skid also would be unavailable; the flight crew continued the approach to landing and used emergency brakes to slow and stop the aircraft clear of the runway.

Narrative

Issue was a Power Brake Failure on approach and landing phase of flight. Flight was a Part 135 revenue flight from ZZZ; to ZZZ1. This was the second leg of the day after a Part 91 reposition leg from ZZZ2; to ZZZ. Preflight inspection in ZZZ2 was normal and did not reveal any issues with the brake system or its components. Taxi checks on both legs did not reveal any issues with either pilot or co pilot brake pedals and pressure. Flight began normally and all phases until approach were normal. We were vectored by ZZZ1 Approach to the RNAV XXR approach at ZZZ2. We were cleared for the approach at 2500 feet MSL in VMC conditions outside of the IF of ZZZZZ. We had the airport in sight and the autopilot was engaged. Once the PIC called for gear down I lowered the gear and we both immediately noticed that the Power Brake Low Press and Anti Skid Inop lights on the annunciator panel did not extinguish normally and remained on for the duration of the flight. This indicates as per the abnormal checklist a 'Power Brake System Failure' The PIC and I both tested our brake pedals and neither one had pressure. We both decided to continue to a landing on runway XXR as it had more than adequate runway available. Runway XXR at LZZZ2 is 6;101 feet long. We briefed that the landing would be using the Emergency Brake Lever. Touchdown was in the touchdown zone of the runway at Vref. PIC NAME utilized the Emergency Brake Lever and brought us nearly to a full stop before taxiway D and we were able to roll clear of the runway on this high speed exit. I as Pilot Monitoring did contact Tower once we were on the ground that we had a potential brake issue and might roll to the end of the runway and exit there. We stopped clear of the runway on taxiway D. We decided to taxi in slowly and made it to the FBO where we shut down and contacted company. Post flight revealed both sight gauges full of fluid and the accumulator was in the yellow arc with battery on indicating a lower than normal condition. When the battery was switched on the accumulator motor was not heard.