The Sun columnist said he struggles with literacy, adding: "I write like a two-year-old and I can't spell."
He also claimed he was "the most disorganised person in the world" during interviews with City of London detectives in 2009.
In tape recordings played at Southwark Crown Court, Redknapp said: "I can't work a computer, I don't know what an email is, I can't, I have never sent a fax and I've never even sent a text message."
He added: "I have a big problem, I can't write so I don't keep anything. I am the most disorganised person, I am ashamed to say, in the world."
Redknapp told officers he had not seen his pay slip in years as he said: "You talk to anybody at the football club. I don't write. I couldn't even fill a team sheet in."
Under questioning over the Monaco account at the heart of the £189,000 bung allegation, the Tottenham manager added: "I pay a fortune to my accountant to look after me you know.
"He writes all the cheques for me and my wife. He pays my bills. He runs my life basically."
Redknapp told officers in June 2009 that the Sun, who he writes regular columns for, "hadn't paid me for 18 months".
He said: "I've never wrote a letter in my life. I couldn't write a letter. I write like a two-year-old and I can't spell."
Redknapp added: "Why am I gonna fiddle 20, 30 whatever thousand pounds of income tax when I walk away six months later from £200,000 that I was due?"
The tape was played out after jurors heard Redknapp made "disastrous" business decisions and lost £250,000 in a "very unsuccessful" takeover bid at Oxford United.
Redknapp lost every penny as part of a loan to take control of Oxford, HSBC executive Alan Hills said.
Redknapp's barrister John Kelsey-Fry QC used the example to deny prosecution claims that the Tottenham manager was a "hard-headed businessman".
He asked Hills at Southwark Crown Court in London: "Do you remember an occasion when he was persuaded to loan, at very short notice, £250,000 to buy Oxford United and that money just disappeared into the mist?"
Hills replied: "I have never seen it, yes."
Hills said Redknapp had shown acumen in the property market, but he agreed with Kelsey-Fry's claim that "with the benefit of hindsight, some investments were disastrous".
He added: "With regard to the shares (in Oxford United)...it is fair to say they were very unsuccessful."
Hills, an associate director with HSBC in London between 2000 and 2009, said he held meetings with Redknapp alongside the football boss's solicitor and accountant.
The jury was told Hills was not initially informed of Redknapp's Monaco dealings in addition to the domestic accounts he held with HSBC.
Hills said: "I would have expected to have known or be told of it."
Redknapp had sole responsibility for the Monaco bank account at the centre of £189,000 bung allegations, said David Cusdin, vice-president of HSBC in Monaco between 2000 and 2005.
Cusdin also described co-defendant Milan Mandaric as "a perfect gentleman".
Giving evidence via videolink, Cusdin said he was aware that Redknapp had flown to the principality to open an account.
"I was certainly aware of his visit - it was quite possible that I didn't open the account, it was one of my team - but I was certainly aware of the visit," Cusdin told the court.
"I don't have a recollection - but I could well have shaken his hand at the meeting."
Both Redknapp, 64, of Poole, Dorset, and Mandaric, from Oadby, Leicestershire, deny two counts of cheating the public revenue when Redknapp was manager of Portsmouth Football Club.
The first charge of cheating the public revenue alleges that between April 1, 2002 and November 28, 2007 Mandaric paid 145,000 US dollars (£93,100) into the account.
The second charge for the same offence relates to a sum of 150,000 US dollars (£96,300) allegedly paid between May 1, 2004 and November 28, 2007.
The court was adjourned until Friday when it will hear from the final prosecution witnesses.
