■ I have a CPL (Commercial Pilot License) with instrument rating and complex and high-performance ratings. The flight began with a good preflight inspection, and we had a good run-up with all good indications with all steps accomplished and verified. Picked up flight following from ZZZ1 to ZZZ2. It was a flight to ZZZ2 in VFR weather with another pilot. During the cruise portion of the flight, I noticed RPMs varying plus or minus 100 from set RPM with some spikes of +/- 200. After troubleshooting without success,

■ The crew of Aircraft X made a normal landing on runway XX at ZZZ, using flaps 40 and normal brake application. Pax (Passengers) were successfully off-loaded. The crew started up for departure to ZZZ1. The SIC (Second in Command) was pilot flying; upon taxi to runway XY in ZZZ he noticed the left brake was ineffective. Both crewmembers agreed.

■ [At FL310], a passenger's battery pack located at seat XX overheated, caught fire, and exploded. A Flight Attendant immediately began fighting the fire, placed the battery pack in a thermal containment bag, and moved it to the aft lavatory. We were notified of a fire in the aft lav by a Flight Attendant, and 15-30 seconds later, the SMOKE LAV SMOKE ECAM triggered on the warning display.

■ On Day 0, Person A and I were sent on a gate call for this aircraft for yellow system hydraulics needing service; we went out and noticed that there was hydraulic fluid all over the belly. We opened the righthand gear door and noticed a large puddle of hydraulic fluid sitting on top of the belly fairing. We then proceeded to run hydraulics and actuate flight controls to try to locate the source of the leak. Nothing was really jumping out, but I happened to notice fluid kind of weeping out of the charge accumulator so…

■ I decided to divert to ZZZ. Once in contact with Approach, per ATC direction I descended into Class C airspace. Shortly thereafter, the aircraft began to indicate abnormal oil temp and pressure on their respective gauges; lost fuel quantity gauge and then fully lost comms other than transponder. Began to troubleshoot. Completed troubleshooting with negative results. After I continued to observe abnormally high oil temperature and pressure indications for the current power setting, combined with the lost comms scenario, I decided to request priority handling. Proceeded direct to ZZZ, was looking for light signals but didn't see any, ensured all traffic on approach was clear and then proceeded to [the runway] threshold and landed.

■ It was requested that the aircraft could taxi to Taxiway 1 from the start of XY to evaluate the issue. PIC took control and agreed with the brake abnormality. Crew made the decision to taxi back to parking and perform a function check and visual inspection. Brake fluid levels were normal; no leaks or abnormalities were observed. Upon taxi to parking, brake operation resumed normal functionality. The check was still made in an abundance of safety. The crew resumed their planned departure from ZZZ to ZZZ1. The crew decided to leave the gear down for roughly 1 minute after departure in the event the brakes were warm and needing additional air flow to cool them, although this was not suspected to be the issue due to normal braking on the previous landing. While flying to ZZZ1, the SIC who was pilot flying noticed the same characteristic, firm feeling that was observed on the ground in ZZZ when the issue was noticed. PIC agreed with this feeling. We agreed with the long runway and additional services at ZZZ1 that we would continue to land. ZZZ Approach was advised of our situation. The crew requested emergency services to be staged on the field in an abundance of caution. The situation was expressed as a non-emergency. Fuel and souls were reported. The QRH was reviewed, and it concurred with the crew’s plan. We were to land flaps 40, slowest possible speed, no brake application. A smooth landing was achieved. Minimal braking was used to exit the runway. Braking to our parking spot, the left brake proved to be ineffective again, confirming our suspicion.

■ We donned oxygen masks in the flight deck as a precaution and we established crew communications.…

■ I immediately requested priority handling stating, “Fire on board.” ATC gave us an immediate vector to ZZZ and issued a descent clearance.… Approximately 3-5 minutes later, the FA called and said the fire was extinguished. We proceeded to ZZZ at 320 kts. Descent and approach were normal. I cleared the runway and set the brakes while the fire crews visually inspected the aircraft. We then taxied to our gate and parked. Passengers were told to remain seated while fire crews and EMTs came on board.

■ …to verify this, I slowly cracked open the Schrader valve and noticed fluid seeping from that as well, which is an indication of an internal leak of that accumulator. We notified our Crew Chief and took the aircraft out of service. I came back to work on Day 2 and was told the aircraft was signed off with no leaks found. The aircraft made one flight and came back here to [gate] XX. It was getting ready to push off the gate for its next flight when we got a gate call for yellow hydraulics quantity low. Person B went out on the call, and I showed him what Person A and I found on Day 0, so he notified our Crew Chief, and we took the aircraft out of service again. I then proceeded to follow the aircraft on the web-based system and saw that they said they could not find a leak. Cause: if I had to guess, it would be due to lack of knowledge of that system on that particular aircraft. Suggestions: more training.