What Makes A Outboard Motor Power Trim Not Work?

When I trim up my 1988 90 HP Mercury, it sometimes sounds like the battery is going dead. If I stop for a second and try again, it will go up more and the same thing happens. This does not happen every time I trim it up. It always goes down fine. The fluid is full.

The fluid has never been changed.

My power trim will power down but not up...any ideas

The trim on my 90 hp johnson stopped working so I used the manual release to get the motor down but I cannot get the motor to tilt manually, I have tried with the manual release open and closed but it won't work. When I try to lift the motor it feels like its locked.

When you hit the switch listen for the pump motor if it makes noise check the hydraulic fluid. If it doesn't make noise its the switch or wiring. Check grounds on battery.