Investigators found an extension lead had been wired into a socket in the room where the fire started, where a storage unit contained items including a games console and a TV, the inquest was told.
Jason Woodman of Mid and West Wales Fire and Rescue Service told the inquest that, "based on the balance of probabilities", the fire had started in that area.
He said there were no other potential source of fire found in the room.
Mr Woodman said there was heat and fire damage under the surface the TV and console were on, adding that “charring” was seen underneath the area, although there wasn’t photographic evidence.
He said the smoke detector may not have sounded because the door of the bedroom was closed.
A photo of the remnants of a TV and games console unit shown in the inquest revealed extensive damage.
Forensic scientist Iain Peck told the inquest he found no evidence of a fault with any of the equipment, including extension cables, a TV and a games console, which had been taken from the first-floor bedroom.
Assistant coroner Kirsten Heaven told the inquest it was “unfortunate” that there wasn’t more detailed evidence, photography and forensic analysis of the area.
Muhammad died from exposure to the flames and things burning around him, the inquest was told.