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.
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.