This sounds likes a trilogy of books based on the Cyborg Commando RPG that were published in 1987/88.
The plot points generally match - blurb from Planet in Peril gives a pretty accurate summary
Cris Holman’s world is turned inside out when insectlike aliens attack and destroy his hometown, murdering his family and his friends.
Motivated by vengeance, Cris volunteers to become a Cyborg Commando, a new breed of soldiers who allow their brains to be removed from their bodies and placed inside computer-operated fighting machines specially designed to combat and conquer the alien menace.
As Cris Holman’s body lies in cryogenic storage, the new Cris is dispatched to help defend the planet – before all of mankind becomes subjugated to the awful plans of the aliens. He and others like him are Earth’s best defense…and its last hope.
The "cyborg commando" bodies have limited energy (batteries) and managing this is a big part of the training. They are also able to shoot lasers and microwaves from their hands, have superior senses & engage in hand to hand combat.
The only difference is that in my (very vague) recollection the main character is not a child - he is a young man, possibly a teen.