Regulator Ofgem said this was too many and has written to energy company bosses telling them they must improve.
The details come from a report for Ofgem which found that 57% of domestic customers who had complained were not satisfied with the response.
Companies must be speedier, communicate better and be more proactive, it said.
Ofgem's chief executive Dermot Nolan said the results of its research were "frankly awful".
He has written to the companies giving them a three-month deadline to carry out an independent audit of their complaint handling process.
Satisfaction with Npower and Scottish Power was particularly low, the regulator said.