Prison inmate Charles Miles gave notorious wife-killer Scott Peterson a beating behind bars earlier this month ... and now he's sharing his side of the story.

In an exclusive preview clip obtained by TMZ, Charles tells Court TV via phone call he went into "attack mode" after Scott rammed into him during a game of pickleball. He says Scott "aggressively" sprinted at him with his paddle in hand --allegedly to chase the ball -- and made no effort to avoid him.

This pissed Charles off, who says he "beat him down to the ground" and "beat the hell out of him." Charles says there was a bit of a struggle, but once he overpowered Scott, he climbed on him and started pounding him.

Despite the fight ... it seems like Charles and Scott are A-Okay with one another. Charles confirms to Court TV they spoke about the brawl the next day to clear things up.

He says he felt it was in his best interest to be on good terms with Scott considering how much money he has ... meaning he could pay fellow inmates to gang up on him.

Believe it or not ... Charles even says he and Scott talked it out for about two hours together directly after the altercation. That is, from isolated cells a few spots down for each other.

Charles claims he even apologized -- saying a "primal urge" was triggered when he saw Scott coming at him full speed ... adding that his anger was intensified over him being a convicted woman and baby killer.

He says Scott tried convincing him of his innocence ... which he has maintained ever since his wife, Laci, was found headless in the San Francisco Bay more than 20 years ago. Their unborn child was separated from Laci when their bodies were found.