The boy was reaching into a freezer when he was electrocuted by a wire exposed by a loose rail which left him with a burn and pain in his chest and leg.
The local Public Protection Partnership said procedures “were not followed properly” after staff were told what happened and the freezer was still being used the next day until it was eventually switched off.
Store records showed the rail was known to be loose and had been patched up with glue and tape before the accident.
A Tesco spokeswoman said: “This incident at our store in Bracknell in July 2017 should not have happened – as we acknowledged in court, on this occasion we did not meet our high standards when it comes to health and safety.
"We immediately refreshed colleague training on our health and safety and maintenance escalation procedures at this store after the incident took place.”
The £536,000 fine also included costs and a victim’s surcharge.
Councillor John Harrison, Executive Member for Culture, Delivery and Public Protection at Bracknell Forest Council, said: “This investigation which followed an incident where a child was electrocuted in the store revealed significant breaches of health and safety legislation and this is clearly reflected in the sentencing.
"The council will always follow up concerns about health and safety matters in premises where it is responsible for enforcement and if anyone has concerns they should contact our environmental health team.”
