"The courts have repeatedly emphasised the importance of respect for the sanctity of the home. As we noted almost 20 years ago, 'conduct of this kind affects the sense of security of the whole community'," the justices said, referencing a 1999 case.
The case they heard in April was for Chase Hutchison.
Today, they released their decision after the Crown said his sentence was "manifestly inadequate".
On three occasions Hutchison had attacked his partner - the first came in December 2015.
At the time he was already serving a sentence of home detention for other charges.
The first incident involved threats with a filleting knife and a struggle saw the woman suffer serious cuts to her fingers and chest, and an assault with a cigarette lighter.
The second incident, in January 2016, involved kicking, stomping and punching in
what the sentencing judge called a "frenzied physical attack".
Hutchison gave his partner Tramadol to relieve her pain, but two days later subjected her to another violent and prolonged beating - this time using a metal bar stool.
The blows tore through the tissue on one of her legs and sent blood splattering on to a nearby door.
These last two incidents left the woman with a perforated eardrum, serious contusions on the back of her head, neck, chin, back, groin and limbs and the need for a skin graft to repair her leg.
She is now permanently scarred and has been diagnosed with post-traumatic stress disorder, the Court of Appeal judgment reads.
"Her physical recovery was lengthy, causing her to lose her job. Her memory has been affected by her injuries. She now lives overseas, in part in consequence of this offending," the judges said.
Hutchison was sentenced to six years and nine months' imprisonment by Judge Bruce Davidson for the attacks, but the Crown argued this wasn't enough to reflect the brutality of the offending.
A sentence indication had been given to Hutchison of eight-and-a-half years' imprisonment. He didn't accept it but later pleaded guilty - some five months later.
At sentencing, Judge Davidson then departed from his indication and sentenced Hutchison to just under seven years with a minimum period of imprisonment of three years and four months.
The judge's sentencing notes read that the victim "almost certainly has been destroyed for life" but that Hutchison was not an inherently cruel man and had reacted with uncontrollable rages.
Treatment of that condition would be "long, difficult, and very, very challenging", Judge Davidson said.
He added that the aggravating features were self-evident, including the use of weapons, that the offending occurred during home detention, previous violence convictions, and "a profound if not life-changing effect on the complainant".
Mitigating considerations, he said, were the guilty pleas - albeit late - and the steps taken to obtain treatment while in custody. There were also psychiatric and psychological reports suggesting the offending was caused by "impulsive rage".
Some credit for remorse was also given by the judge.
The Court of Appeal judges, however, said violence occurring in the victim's home will normally also be considered an aggravating factor.
"One cannot realistically or effectively lock the door against a co-occupant. Where the victim is a family member, dependent on the offender for emotional and physical support, the alternative aggravating factor of vulnerability almost inevitably will be triggered. It would be a rare case of family violence where that was not so.
"We therefore find that the sentence imposed, six years and nine months' imprisonment, was manifestly inadequate, and requires correction," the appeals court judges ruled.
They substituted it with a sentence of eight years and six months' imprisonment with a minimum period of imprisonment of four years and three months.
WHERE TO GET HELP:
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.
OR IF YOU NEED TO TALK TO SOMEONE ELSE:
• LIFELINE: 0800 543 354 or 09 5222 999 within Auckland (available 24/7)
• SUICIDE CRISIS HELPLINE: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• YOUTHLINE: 0800 376 633 ,free text 234 or email talk@youthline.co.nz or online chat.
• NEED TO TALK? Free call or text 1737 (available 24/7)
• KIDSLINE: 0800 543 754 (available 24/7)
• WHATSUP: 0800 942 8787 (1pm to 11pm)
• DEPRESSION HELPLINE: 0800 111 757
• SAMARITANS – 0800 726 666.
