Mr Balls, who lost his seat in May, told the Daily Telegraph it was "no secret" he thought Mr Miliband had to position himself better with business.
In the interview, Mr Balls said he had not been in the "core campaign team" around Mr Miliband for the election.
He added that since the election he had turned down an offer to appear on ITV's I'm a Celebrity... Get Me Out Of Here!
"I'd already subjected myself to one high-profile public vote this year, and I wasn't really sure that I wanted a second one," he said.
On Labour's approach to business going into the election, Mr Balls said he had publicly supported the energy price freeze pledge, even though he thought it allowed the party to be seen as "anti-business".
"What I didn't like was the language giving the impression that energy companies are the bad guys," he said.
"If you allow yourself to be anti-business, or anti-bank or anti-energy company, people think, 'Hang on a second, you have to work with these people if you want to govern.'"
Mr Balls said he had to "take it on the chin" that he had not been able to persuade people he could run the economy.
He lost his Morley and Outwood seat in West Yorkshire to Conservative Andrea Jenkyns by 422 votes on 7 May.
He revealed that among the messages of consolation he received after his defeat was a "very nice" text from Chancellor George Osborne, but nothing from David Cameron.
Mr Balls said he was not now tempted to return to front-rank politics, having spent 20 years as Gordon Brown's adviser, then an MP and cabinet minister, before being shadow chancellor on Mr Miliband's front bench.
"I'm not going to the House of Lords, and I'm not planning to go back to the Commons," he said.
"It's a new chapter for me and there will be something for me outside politics."
Since the election he has turned down offers of work except for part-time academic posts at Harvard in the US and at the London School of Economics.
On the Labour leadership contest, Mr Balls said his wife Yvette Cooper was standing as a candidate because she is "there for a purpose".
Former shadow chancellor Ed Balls has attacked Labour's approach to business under Ed Miliband.