Police and paramedics found Harvey Tyrrell unresponsive in the back garden of the King Harold pub in Romford, Essex, in September last year.
He was rushed to hospital but was pronounced dead just over an hour later.
It was initially believed Harvey, from Romford, had died from hitting his head during the fall.
But on Monday police confirmed his cause of death as electrocution following a special post-mortem examination at St Thomas’ Hospital.
Two men, aged 70 and 72, have been interviewed under caution over Harvey’s death, and a file of evidence has been passed to prosecutors.
An inquest into the youngster’s death is expected to begin on Tuesday.
A Met Police spokesperson said: “Officers and LAS attended and a seven-year-old boy, Harvey Tyrrell from Harold Wood, was found unresponsive.
“He was taken to an east London hospital where he was pronounced dead at 18.33hrs.”
A police spokesperson said a file on the incident had now been sent to the Crown Prosecution Service.
A fundraising appeal set up online described Harvey as “a beautiful, happy and healthy seven-year-old boy who loved his football just like any other boy his age”.
Expressing his thanks to donators, dad Lewis Tyrell later wrote: “I can not express how overwhelmed myself and Danielle are by the support and love that has been given to us at this darkest hour.
“Through our tears we have read every single message individually and you have given us the strength to carry on when we thought we were too broken and weak to carry on.
“Thank you and god bless you.”
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