The Livingston-based firm, which provides industrial gas meters, said that all resolutions had passed at the meeting but did not give further details on who attended or voted on the day.
The company has been listed on the main market of the London Stock Exchange since 2012 and has more than 27 million shares in issue. Investors holding nearly 3.7m shares, or about 13.5 per cent of the total, had cast their vote by proxy two days ahead of the meeting.
The company turned down a request for the media to attend the annual general meeting in the City of London, telling the Herald: "The AGM is for the purpose of shareholders."
Its largest investors include Macquarie Bank, which holds almost 30 per cent of the firm's stock; Old Mutual Global Investors, which holds just less than 10 per cent; Henderson Volantis Capital; and British Steel Pensions.
"The company's decision and their approach to voting disclosure are very disappointing and do not reflect expected best practice," said Sarah Wilson, chief executive of Manifest, the proxy voting agency.
A spokesperson for PIRC, Europe's largest independent corporate governance researcher, said that "as a general principle, meetings of public companies should be open to the media on the basis of good governance and transparency".
Last week, cloud computing business Iomart also came under fire after it barred reporters from its investor meeting, blaming restrictions around its possible takeover by an IT company controlled by the private equity group Cinven.
While companies have no obligation to allow non-shareholders into their meetings, many corporate governance groups view open access as best practice.
Energy Assets, chaired by former Aggreko boss Dr Christopher Masters, has a market value of £109m.
The firm said in a statement yesterday that trading "continues to be encouraging" following the takeover of BGlobal Metering, which doubled its portfolio of meters in April.
"Integration of this business into the group is progressing well," it said.
The company also won a contract with British Gas in July to install advanced meters for about half of the group's industrial and commercial customers across the UK.
By the end of July, Energy Assets was looking after a portfolio of 327,000 meters and other data assets.
The firm refinanced its £10m debts with Macquarie last year when it signed a new £35m loan facility with Bank of Scotland.
The firm hopes to expand further as more firms upgrade their infrastructure. The UK Government is pushing for meters in every home and business in the country to be smart-enabled by 2020, allowing remote monitoring and feedback on energy use.
Last month, energy regulator Ofgem said 86 per cent of larger corporate premises now have advanced gas meters, while 75 per cent have advanced electricity meters, though the roll-out has been slower than the regulator had hoped.
The watchdog will soon set targets for suppliers to switch their corporate customers to fully smart meters ahead of the 2020 deadline.
For the year to the end of March, Energy Assets posted a 34 per cent rise in revenues to £24.2m, while operating profits increased 38 per cent to £9.8m.
Shares in the company closed flat at 402.5p yesterday.