These were a nasty surprise for the Wehrmacht. I read one account where a single KV1 held up at least a battalion if not an entire panzer regiment for hours. They eventually were able to take it out after it got dark with infantry and satchel charges.
That was a KV-2 with a 152mm gun. It slid off the road, the ONLY supply road, for one of the panzer divisions. Took a couple of days to get it out. Some of the KVs didn’t even have ammo so they literally ran over German 37mm AT guns. Most were lost when they ran out of fuel.