The Briton completed 91 laps and set the day's best time around the floodlit Sakhir circuit of one minute 29.545 seconds.
The time was slower than the 1:29.348 recorded by Williams' Carlos Sainz on Thursday. The Spaniard's teammate Alex Albon was third fastest on Friday, 0.105 off Russell's pace after a massive 137 laps.
Four-time world champion Verstappen did a full day and ended up 0.021 off Russell's pace.
"There were a few little problems but overall, we completed quite a bit of what we wanted to do. I think it wasn’t bad but at the same time there is still a bit of work to do," said Verstappen.
Australian Oscar Piastri was fourth for champions McLaren, who have done a good job of staying under the radar by showing flashes of speed but aborting laps that could have put them up in lights.
"We tried a lot of things and learnt a lot. Some things felt quite good, others still need improvement but working through this is exactly what testing is for," said Piastri.
"The car ran pretty much faultlessly, which was a solid place to be starting from. We've got a lot to review before Melbourne, but I think we’re going into it in decent shape," he added referring to the season opener in Australia on March 16.
Red flags
Ferrari's Charles Leclerc was fastest in a four-hour morning session bizarrely interrupted by a pane of glass falling out of the starter's box and shattering on the track.
That was followed by another red flag in the afternoon when a bus appeared on the run-off area as some cars were on the track.
Seven times world champion Hamilton was sixth overall for Ferrari, behind Alpine's Pierre Gasly in fifth, after finishing earlier than planned with 47 laps.
"Overall it’s been a great few days and we’ve made some strong progress as a team," said the Briton. "We’ve managed to gather a lot of good information to build on before the season starts."
Mercedes' 18-year-old Italian rookie Andrea Kimi Antonelli was second in the morning, 0.077 slower than Leclerc's best lap of one minute 30.811 seconds, but dropped down to 10th overall at the end.
"It's hard to know what fuel loads everyone is running, as we're all doing our own different programmes, so you have to take everything with a pinch of salt," said Hamilton of what he had seen so far.
"McLaren won the constructors' last year. We expect them to be one of the quickest, if not the quickest, as with Red Bull, who dominated for many, many years."
Aston Martin had a day of changes, with Lance Stroll initially reported unwell for the morning session and Fernando Alonso driving instead.
The Canadian returned for the afternoon but then felt unwell again after 34 laps and Alonso stepped back in for the final hour.
"Initial feedback from Lance and Fernando suggests we have made progress with the driveability of the car, but we have also discovered areas that could be better and need more focus," said team principal Andy Cowell.