Lance Bain loved Ferraris, but after an argument with his partner over a car he was attacked with a mallet and left with a leg wound that became infested with maggots.
He went to hospital 11 days later where he eventually died of a bacterial infection.
Mr Bain's partner Natalie van Breugel, also known as Natalie Reader, had originally been charged with manslaughter which carries a maximum penalty of life in prison.
However, at her brief appearance at the High Court at Auckland today, the Crown downgraded the charge to injuring with intent to injure which has a maximum of seven years in prison.
The 45-year-old pleaded guilty to the charge and will be sentenced in March.
Justice Sarah Katz ordered a pre-sentence report which will look at the possibility of home detention and continued van Breugel's bail over the Christmas period.
According to the police summary of facts, Mr Bain was sleeping at van Breugel's home in November last year when she attacked him with a mallet.
She was furious at Mr Bain for selling a car that she believed was at least partly hers and she did not want to sell.
She had also seen text messages on Mr Bain's phone from a woman police describe as a "female associate".
Van Breugel struck Mr Bain repeatedly with the mallet, hitting him in the arms, torso and legs and left him with bruises on his arms and his left leg.
Later that day the argument continued and it was loud enough for neighbours to call police.
Mr Bain got in his car to leave van Breugel's place and she thumped on the window with her fist and yelled something like: "Open the door you f***ing bastard, I am going to kill you..."
About half-an-hour later, police pulled him over and breath-tested Mr Bain. He was nearly four times over the limit, recording a level of 1573 micrograms of alcohol per litre of breath. The legal limit is 400mcg.
Police noticed the bruising to Mr Bain's body and offered to get him medical help but he declined.
It was not until 11 days later on November 28 that Mr Bain was taken to hospital.
Police say the leg wound was "infested with maggots" and he had developed a bacterial infection. His alcohol reading on that day was similar to the breath-test taken by police.
Five days later Mr Bain died. According to police, his alcoholism had left him vulnerable to the bacterial infection which eventually overwhelmed his body.
A Friend of Mr Bain told the Weekend Herald in December last year that the 43-year-old had made his fortune selling cars and in property but lost millions in recent years after a difficult break-up with with his wife Michele.
He had once owned two red Ferraris and lived in some of Auckland's most exclusive suburbs but lost all his properties in mortgagee sales.
In 2005, the family featured in a Herald property story which said the family were moving out of their $2 million Orakei home because it was too big for them.
That house had a gym, internal courtyard with fireplace, air conditioning in three of the four bedrooms and a projection TV as well as views of Hobson Bay, the city and the harbour.