Mercedes completed the most laps of any team in the opening winter test at Jerez last month, racking up 309 - 58 more laps than nearest rival Ferrari.
"Today we didn't get as many laps as we would have liked, because we know the car can go further," said Hamilton.
"But when you look at the full picture we are at the top of the mileage [chart], so I'm really, really happy with that.
"Although it looks like we are doing a lot of laps, it's still a massive challenge for us.
"We are still coming across issues and things that we are finding out about the car.
"But it looks like other people are having issues and some are bigger than others."
Bahrain test day one report
While six of the teams covered over 60 laps each on Wednesday, Red Bull, Toro Rosso, Lotus, Williams and Marussia all failed to get above 15, with the latter quartet in single figures.
Hamilton was third quickest, a second down on pacesetter Nico Hulkenberg's Force India.
The Briton said Mercedes had yet to pay much attention to outright performance.
"At the first test we were obviously trying to get mileage on the car and not really focusing on the performance, but we will begin now," he said.
"It's very difficult to know where we are in terms of performance, but in terms of going the distance we are there at the front.
"If you look at the times at the moment it's all Mercedes at the top."
AUTOSPORT Live coverage from the Bahrain F1 test resumes at 6am UK time on Thursday