The Otherworld (Underdog Book #4‪)‬

After battling the hyenas, Eric gets a notification that something called a Place of Power has been found. That is the only clue that might help him get back to his native world. 

But there's a problem. The system needs mana to calculate a route. Eric simply doesn't have any and he doesn't know when he will. That is because, due to the strange laws this world lives by, Eric's mana supply isn't filling up. But the Great System also exists here, though its laws are only partially functioning. 

Having found himself in this alien and dangerous world without magic or the support of his loyal Gorgie, Eric understands that the kid who saved him, Badger, is currently his only source of useful information. That is a chance to understand and gain knowledge about this world and, in all likelihood, find a way to rustle up some mana.