The largest force the Russians seem able to organize is the BTG (Batallion Tactical Group). These are supposed to have 200 infantry, 10 tanks, 40 infantry fighting vehicles, and possibly some mobile artillery - but most sent to Ukraine were already short on these items, and have become progressively shorter.

This is how a BTG operates: when advancing against the Ukrainians, a small swarm of untrained recruits are sent out ahead of the main force with light weapons. When they encounter Ukrainian defenses, most of them are killed immediately.

Now the main force knows where the Ukrainians are, and opens fire with tanks and artillery. It matters to them not a whit if their own troops are still in the target area. They are totally expendable.