Complex sentence: The investigation into the accident, however, found the cause was spatial disorientation following the loss of a flight instrument after both generators failed after the exhaustion of power from the battery, due to the crew using an outdated checklist and not adhering to a checklist.
Split into simpler sentences: The investigation into the accident, however, found the cause was spatial disorientation following the loss of a flight instrument after both generators failed. Backup battery power was exhausted early, due to the crew using an outdated checklist and not adhering to a checklist.