Date: 201507
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Dash 8 Series Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Takeoff / Launch
Aircraft component: Engine Control
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Physiological - Other; Confusion; Fatigue
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Rejected Takeoff; Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Human Factors; Aircraft; Weather
Primary problem: Aircraft

Narrative: Aborted takeoff XB:25 local; Runway 15L; max speed was 25 knots.Flight was an originating flight out of ZZZ. When we; the crew arrived at the aircraft; it was extremely hot onboard at XA:30. The APU was Mel'd. I asked operations if we could either hook up a cooling cart or start an engine before boarding passengers as I felt it would be dangerously hot to put passengers onboard and then shut the door for pushback. They agreed. I called my dispatcher and told him that we would probably be late off the gate as I felt the need to do this. He agreed and so we started the no.2 engine and got air flowing prior to boarding the passengers. All operations were normal taxiing out with the nose wheel tiller. We were cleared for takeoff on runway 15L. Immediately upon adding power the aircraft veered to the right. I Captain (CA) the pilot flying used rudder and some brake to bring the aircraft back to center. (I thought initially maybe the nose wheel was not straight from the taxi out). Upon straightening the nose wheel; I added more power and immediately the aircraft veered to the right. I aborted the takeoff and my FO notified tower of our rejected takeoff. We taxied off the runway with the nose wheel tiller. We waited for a gate until XC:47. We taxied back to the gate and deplaned passengers. I called my dispatcher and spoke with maintenance and it was decided that we would do a run up. During the run-up the right engine was developing power at a slower rate than the left engine. It was determined that the ECU was not operating correctly. We selected the right ECU to manual as per maintenance and then ran a high speed taxi down Runway 15L as per maintenance request. The aircraft operated as a 'normal' ECU inop operation would. We taxied back to [the gate] and shut the airplane down.The entire crew went inside the terminal as we were all extremely overheated and needed to cool down. The aircraft did not have an APU and we had been on the aircraft over 2.5 hrs including this maintenance run. (The flight deck was about 120*F) It was determined that we would ferry this aircraft to ZZZ1 so I (CA) went back down to the aircraft to await the ferry permit and associated logbook entries. I thought I was hooked up to the GPU when I brought the Batt Master; Main and Aux batteries online. I just can't remember this sequence. In any event; I was sitting in the back of the aircraft as my First Officer (FO) joined us on the aircraft; went up front and called me to tell me that the GPU was offline and batteries were depleted to about 16volts. I called maintenance and told them what happened and that we would be further delayed until we could bring the charge back up and also cool the batteries down.I felt very foolish allowing this to happen. In retrospect; once we deplaned the passengers; I should have called for an air-cart. I didn't think it would be very long before we did our maintenance run but it was 'very long.' From the time we deplaned until we returned from our run up; it was 2.5 hours in an extremely hot cockpit. I think this may have been an extenuating circumstance in my neglecting to notice that the GPU was offline. In the future; if I am on GPU power only; I will go upfront every 15 minutes to make sure everything looks normal.


Second narrative: [Report narrative contained no additional information.]


Synopsis: The flight crew reported that during the takeoff roll the aircraft started to veer off the runway centerline. The takeoff was rejected and the aircraft returned to the gate where the problem was diagnosed as a faulty engine control unit (ECU) on the right engine. It was determined that the aircraft would be ferried for further maintenance. However; due to extremely hot ambient temperatures; and lack of a ground power unit; the aircraft batteries overheated and were inadvertently depleted below the minimum charge.