How could Ash's Pikachu loses

[Samike360]

How could pikachu be only level 35-37 he has battled through kanto, johto, orange islands, hoenn, battle frontier and currently sinnoh??

I bet that if you went and approximated the experience points gain of all the pokemon that pikachu has beaten it would not be above lvl 40 at all. And no, Regiice and dragonite are probably no more that lvl 50 themselves, and many of pikachu's wins have been shared with other pokes.

 

[Vernikova]

I bet that if you went and approximated the experience points gain of all the pokemon that pikachu has beaten it would not be above lvl 40 at all. And no, Regiice and dragonite are probably no more that lvl 50 themselves, and many of pikachu's wins have been shared with other pokes.

Levels aren't included in the anime. If they were, then Pikachu would beat every Gym Leader and no Pikachu doesn't "Reset". That doesn't exist in the anime either.

 

[Vance09]

Well, there are apparently no levels in pokemon, and pikachu refuses to evolve. And it would be funny if there were levels, because then pikachu would have tons of exp.
A wild James appeared!
Go Pikachu!
Pikachu used thunderbolt!
James was defeated!
Pikachu earned 99999 exp!

 

[Ayselipera]

Because if Pikachu always won in the show it would be more predictable then it is now. They have to add in a little diversity.