50 HP outboard power pack issue?

Hello! New member here. I have a 2008 Mercury 50hp 2 stroke outboard. It's been running great. Yesterday I had it out in the ICW and it gave me some issues. At first it seemed like either it wasn't operating at full power or the tilt wouldn't go all the way down. I slowed down took a look. This issue just went away. Later in the day I was running wide open throttle and the motor just quit. Like I ran out of gas. I didn't. I was able to restart the motor and jog back to the marina. No problems at low speed. I was low on oil so I added some. I don't think that was the issue. I stated it back up and went for a test run. Same thing. Cut off at full speed. This time the motor was dead for a minute. Tilt and trim wouldn't work. Wouldn't turn over. Nothing. It was like I disconnected the battery. Then all of a sudden the power came back and I could restart the motor. The only thing I did recently was change the battery. I had this battery on there before. I did hook it up backwards for a minute. I noticed it when the tilt buttons went the wrong way. I swapped back within a few minutes or so. It sparked a couple times. Not sure if that matters. All that to say, can any smart person out there tell me what they think the issue is? Power pack? Something else electrical?

You may have damaged the switch box or coil ignition thingees.

Are you using those worthless wing nuts to hold the cables to the battery? If so, replace them with stainless nuts and a flat washer. That can cause expensive problems when they don't make a solid, reliable connection.

Jeff.