The Battle of Koyeset occurred in 1.5 ABY on Mustafar. HK-47 and his droid army attempted to wipe out the Koseyet Mining Camp, as part of HK-47's personal mission to seek revenge on all organic "meatbags" for their part in the events that caused him to lose his original body. HK-47's army consisted of AK-1A "Hammer", AK-3 "Reaper", GK-5 Sentry, and HK-77 droids, which HK-47 either recruited to his side or built himself. When HK-47 attacked the mining camp, he was eventually repelled by a group of spacers, who destroyed his droids and drove him back to the Droid Factory, effectively ending the Battle of Koseyet.
The Battle of Koyeset started after a group of spacers escaped HK-47's Decrepit Droid Factory. They talked with the miners at the camp, and began to prepare for the battle to come. The spacers needed to keep the camp intact. Their secondary objective was to protect the generators around the camp, or else they'd be at an immense disadvantage. The miners weren't well trained or armed, but they were willing to fight to the death to defend Koseyet. A spacer used this to his advantage, and ordered the miners to defend key points. Another spacer, most likely a commando or mercenary of sorts, had the opportunity to place explosives around the camp. With barely enough time to strategically set up the miners and charges, the first waves of HK47's army fired upon the camp.
With the battle now underway, all the men fought bravely to defend Koseyet. Many miners died at the blasters of HK47's newer droids. Over 100 HK-77's were destroyed, along with many of the AK-3's, GK-5's, and AK-1A's. Near the end of the conflict, the Forward Commander entered the fray. He was by far the deadliest droid on the battlefield, possessing the ability to command other troops and his own personal escort. With the remaining miners and spacers focusing their fire on him, the Forward Commander was obliterated. This one act gave the rest of the survivors a huge moral boost. The remaining men charged fearlessly with boosted egos and easily wiped out the few remaining droids.
The Battle of Koyeset was a victory, but HK-47 was far from stopped. The surviving spacers left the camp and raided HK-47's new factory in a hope to end the conflict.