Max Verstappen endured two contrasting sessions in Melbourne on Friday while fellow F1 rookie Carlos Sainz Jr had a "positive day".
The 17-year-old Verstappen, who is making history in Australia as he is the youngest driver to take part in a full race weekend, was sixth fastest in the morning and completed 31 laps of the Albert Park circuit.
However, he only clocked six laps in the second Free Practice session after his Toro Rosso picked up a battery problem.
"This morning we were able to complete many laps and it was good for me to get used to the track," the Dutch youngster said. "It was a useful first practice and I was able to understand the car a bit more. I also didn’t make any mistakes, so that was good.
"This afternoon unfortunately we were not able to spend much time out on track due to a battery issue. The team pushed very hard to send me out again but we ran out of time. It wasn’t the best end to the day, but we will check the data tonight and hopefully we can make the best out of tomorrow’s third and final practice session before my first ever qualifying session of the year."
Meanwhile, his STR team-mate Sainz Jr enjoyed a problem-free day in the STR10 as he completed 32 laps in the morning and another 42 later in the day.
"I’m happy with today, I had been waiting for this day for a very long time and it was definitely a decent first day," the Spaniard said.
"We covered a lot of mileage, which was obviously our target for today as I am a rookie and new to this circuit. I enjoyed it a lot out there. Now we need to go through all the data we gathered today and keep improving.
"I feel very comfortable in the car. It’s a challenging track, but I like it and all in all it’s been a positive day."