Updated

A Sydney man pleaded guilty Tuesday to severely burning his girlfriend’s 10-month-old son in a bathtub filled with hot water -- and leaving the baby unattended so the man could smoke a cigarette and charge his cellphone.

The baby was burned on 40 percent of his body. He was hospitalized for almost four weeks, ABC Australia reported.

Altare Tepania, 24, was looking after the child while the baby's mother was shopping, according to a statement from prosecutors and defense lawyers obtained by News Corp Australia. After the child vomited, Tepania put him in the bath to wash off.

MICHIGAN MOTHER CHARGED WITH KILLING BABY BOY

“I put him in the f****** shower and I didn't turn the cold on; I only turned the hot on. I left,” Tepania reportedly told police at the scene. "I went and put my phone on charge. I had a smoke too."

"I don't know what I was thinking,” he said. “I don't know...not thinking straight today."

After hearing the baby screaming, Tepania returned to the bathroom to find the child lying on his back under the scalding tap with his skin peeling off, according to the statement.

Tepania picked the infant up out of the bath by one arm and dropped him on the tile floor, fracturing his elbow and causing injuries to his face and head. He then took the baby to the bedroom and poured cups of cold water on the baby.

BABY LEFT IN SMOKE SHOP PARKING LOT

He also tried feeding the screaming infant a bottle of formula but when the baby spat it out, Tepania forced it into the child's mouth with such force the baby's mouth bled. Court documents say Tepania also struck the boy at least once.

When the boy’s mother returned home shortly after, she said Tepania had a strange look on his face and told her not to call for help. Ignoring him, she put the baby in a cold bath and called emergency responders.

Tepania later told police he was hungover “really bad,” and was a "10" on a scale of one to 10, with 10 being the most hungover. He said he had been drinking and also tested positive for methamphetamine.

Since the incident, the baby has healed without scarring and there aren't likely to be long-term effects, according to court documents.

Tepania was supposed to face trial Tuesday but instead he pleaded guilty to two charges of recklessly causing grievous bodily harm and assault occasioning actual bodily harm.

The original charges carried a maximum 25-year sentence, but, after reaching a deal with prosecutors, Tepania’s sentence was reduced to 15 years.

Tepania is due back in court in October.