A weak battery or low battery voltage can cause the transmission to enter into fail safe mode. This will cause a loss of power because the transmission will be locked in third gear.Google+
Car Problem Reports
Nissan Sentra Weak Battery May Cause Transmission to Enter into Fail Safe Mode
Nissan Sentra Problem
Average Mileage: 135,500 mi (95,000 mi - 176,000 mi)
Visitor, 2001 Nissan Sentra, 176,000 mi
Battery when dead a few days later. I replaced the battery and no more problem, tho I didn't know it would correct the power problem.
Visitor, 2000 Nissan Sentra, 95,000 mi
Just after I purchased this car used I found that sometime it would stay in third gear. I replaced the battery and the problem was completely resolved.