Data from FlightRadar24 showed the flight cruising at 36,000ft when almost three hours into its journey, over the Adriatic Sea, it took a sharp left-hand turn and landed 20 minutes later.
It is understood there was no issue with the power bank, but regulations state power banks are not allowed to be charging in the hold during a flight.
A spokesperson for the airline said: "The aircraft landed safely and passengers disembarked routinely and we provided hotel accommodation and meals where available. As some customers remained in the airport, they were provided with refreshments.
"The safety of its passengers and crew is EasyJet's highest priority and EasyJet operates its fleet of aircraft in strict compliance with all manufacturers' guidelines.
"We would like to apologise to all passengers for any inconvenience caused by the diversion and subsequent delay."
EasyJet's rules, external state that power banks are accepted on aircraft in cabin baggage only but are "prohibited from use" and "must not be used to charge other devices".
A maximum of two power banks per customer are allowed, they must not exceed 160 Watt-hour (Wh) for lithium batteries and they must be individually protected such as in their original packing or a plastic bag.
Announcements are often made by cabin crew warning against their use.
Other airlines have brought in similar rules.
Ryanair, external says power banks are not allowed in checked baggage, cannot go in overhead compartments, and must not be used to charge or power other portable electronic devices during taxi, take-off or landing.
British Airways, external says power banks must not exceed 100Wh, they must be stored in the seat pocket or a bag placed under the seat in front, and plug sockets on planes cannot be used to charge power banks themselves.
The strict rules reflect the fire hazards of lithium-ion batteries - which most power banks use. They carry a risk of overheating or catching fire which is easier to deal with in the cabin than in the hold.
Data from the UK Civil Aviation Authority shows that in 2024, two flights a week globally experienced "thermal runway incidents" to do with lithium batteries, which includes incidents such as passengers reporting leaving power banks in their hold luggage and battery fires.
The International Civil Aviation Organisation, a UN agency, introduced new restrictions, external for power banks in March.
A man caught fire at Melbourne international airport in November 2025 after a lithium power bank in his pocket ignited, leaving him with burns to his leg and fingers.
In January 2025, authorities said a portable power bank was the likely cause of a fire that destroyed a passenger plane in South Korea, leaving three people with minor injuries.