It can depend on the game, but generally you have to groom and feed your pet regularly and win battles. Make sure you find out which food your Pokémon likes...
If the battery was working well when disconnected, then either its connections are dirty or a cable is about to break off. I mention the cable because disconnecting often can...
This could be any number if things. Combustion is starting the truck, but then it's being inhibited by something, fuel line or battery issues, perhaps. Take it to a diesel...