Engaging Pengbot Maximus in melee is ill-advised. Stay out of its melee range.
Pengbots will respawn throughout the fight. Take note that all pengbots will die when you destroy one of them. Of particular note are the Pyro Pengbots, who would deal significant damage if they get close to you, and the Cryo Pengbots who would freeze you on the spot. Sometimes Medi Pengbots spawn; they heal you like the Restorative Barrels, so meleeing them keeps your Health and Power up. However, they are now either discontinued or made exceedingly rare. Keep the target locked onto Pengbot Maximus instead, as you would be doing a lot of running.
Pengbot will periodically do a Lethal block-breaking spinning attack, where it will spin in a straight line, dealing multiple 200s and knocking you down. Avoid it by moving / rolling to the sides, but take care as the attack has more range than its animation implies. Make sure to use all Supercharge abilities first as the second phase is easier to fight.
Trying to use healing barrels is generally counterproductive as it requires you to stay in once place, taking more damage than you could heal. It is best to sustain yourself with soders before Maximus reaches 50% health.
At 50% health, Pengbot would stop doing its Lethal spin attack, and would lunge to pummel the ground, hitting 50~60.
It also uses a Heat Vision-esque attack that deals minor damage and grounds a player.
Above all, be patient. This fight can be a long one if your combat style is melee-focused.