The RAC Foundation was testing an Energy Saving Trust claim made four years ago that the installation of more chargers made it possible the complete the circular Highland route in a battery-powered vehicle.
However, researchers said more than half the chargers they tried to use on the route and other Highland roads were out of action or unusable because of connection problems.
They also discovered that using a phone app to access chargers often failed to work because of poor mobile reception.
However, Dr Ivo Wengraf, the foundation’s research and data manager, said that while his experience showed electric motoring in the Highlands was a potential nightmare for visitors, it had significant advantages for residents.
These included free electricity in a region where petrol and diesel can be significantly more expensive than in cities, and space to charge at home.
Dr Wengraf encountered problems with 12 of the chargers he attempted to use during a ten-day trip in September which started and ended in Inverness.
They included chargers not working, others being out of action because the business where they were located was closed, or problems with the app.
On one occasion, Dr Wengraf resorted in desperation to searching public toilets at Scourie in Sutherland for a household 13 amp socket to plug his BMW i3 into.
Dr Wengraf said the car completed the journey without having to use its range extender [back-up petrol engine], “but it had, at times, been very touch-and-go”.
He said he had made a major error in relying on an app to activate the chargers rather than buying a £20-a-year Radio Frequency Identification (RFID) card.
The researcher said: “Deciding, after speaking with ChargePlace Scotland [which operates the public charger network], to save the twenty quid for a twelve month RFID card and rely on the app was possibly the biggest false economy I’ve ever made.
“With a simple RFID card, the rest of the trip would have been straightforward – as it isn’t hampered by IT and communications failings in the same way as the app.
“The enthusiasm of the electric vehicle charging industry for apps is, frankly, inexplicable in Britain where the mobile signal coverage is, on a good day, somewhere between mixed and patchy.
“If others are to be persuaded to experience the North Coast 500 by electric vehicle then surely the advice to all should be to shell out the £20.
"Having multiple cards for multiple accounts is more than a bit of a pain, so would it really be too much to ask of the industry to find a way to let us have a single card that works for all, throughout Britain?
A Transport Scotland spokesperson said: “We are aware that signal can be poor in remote areas and are working with the network operator to resolve this.
“We continue to work to strengthen and expand the ChargePlace Scotland network so that drivers across Scotland can confidently travel the country in an electric vehicle.”
The agency said the charging network averaged 91.25 per cent availability between April and September.