As far as I am aware, there are no dedicated British cemeteries on American soil from the Revolutionary War. There are however many cemeteries that have small sections dedicated to British soldiers.
Often, after a battle, long trenches would be dug, and fallen soldiers would be tossed into the trenches and buried. They usually would not bother putting up any kind of marker. In other cases, individual graves would be dug, bug again, markers would often not be placed. Sometimes today people will dig for some reason (new construction, adding a water pipe, etc) and will run into one of these old graves.
Trenches and mass graves were used in the Civil War as well, but after the war there were funds set up so that relatives could pay to have the fallen returned home and properly buried.
About the only thing consistent among the soldiers was that they were young and inexperienced. The British did have one of the most well-trained armies at the time, though, and even with a lot of inexperienced troops, their training made them a formidable force. Fighting back then was brutal. Muskets weren’t used like modern rifles. They were fired in mass volleys, and then the troops would charge with their bayonets. Close-up bayonet fighting was crucial, as was maintaining lines and military discipline. George Washington got his backside kicked up and down the battlefield initially, mostly because his men hadn’t been properly trained in bayonet fighting and the importance of maintaining lines. Washington got his men properly trained during the misery of Valley Forge, and only after that could his troops really go toe to toe against the British. Overall, close-up bayonet fighting accounted for roughly a third of all battlefield casualties. Brutal bayonet fighting was a standard part of battle. Bayonets didn’t become last-ditch weapons until the Civil War.
The British troops were also very well equipped, something that you definitely could not say about Washington’s troops.
The British had a lot of colonies, and one of the reasons they lost the Revolutionary War was because we weren’t one of the important ones. The British could have sent a lot more troops, and if they had sent 100,000 instead of just 40,000, I think the war would have turned out differently. But that would have meant pulling soldiers out of much more valuable areas, like the West Indies and its valuable sugar trade. The British weren’t willing to risk these more valuable colonies, and so they fought the Revolutionary War with a much smaller force.
The British also had a very thin army, considering how much territory it controlled. Every time a war would start up, the British would find themselves short on trained soldiers. They filled in some of the gaps during the Revolutionary War by renting soldiers from various German principalities. These were generally referred to as Hessians, even though a lot of them did not come from Hesse-Cassel or Hesse-Hanau. The British also hired mercenaries to help with manpower shortages.
There is a tendency in schools to oversimplify history, and they often make it out like most of the U.S. supported the revolution. In reality, only about a third of Americans really supported the revolution. Another third or so wanted to remain British, and the last third really didn’t give two hoots one way or the other. Once the revolution started, those who had been vocal about remaining British all of a sudden grew very quiet. Some stayed in place (with varying degrees of success), some fled to Canada, and some of the men enlisted into the British Army and fought against their fellow Americans. This also helped with the manpower shortage that the British faced.
While the rank and file troops tended to be young and inexperienced (though well-trained), the non-commissioned officers were battle-hardened veterans. Officers also tended to be experienced.
The British Navy had conscriptions and used impressment, but for the most part the Army did not. Soldiers willingly volunteered because they were poor or out of work. If you are living in miserable poverty, there is a certain appeal to steady pay and regular meals. Sure you might get shipped off to some remote corner of the world and might even get into battle, but you took your chances. It was better than starving to death on the street corner. A lot of the soldiers looked forward to their service. It was a chance to see different parts of the world and to go off on a glorious adventure.
The American troops in the British Army had a very high motivation level. They were fighting to keep their homes and their lands British.
History is kinda funny with respect to the Hessians. On one hand, they were very well trained and very disciplined, and had a reputation as very fierce fighters. On the other hand, they weren’t British, and so the British tended to look down upon them. When battles went well, the British praised the Hessians, but when battled did not go well, instead of blaming poor British tactics or poor battlefield decisions, the British would instead blame the Hessians, calling them incompetent drunkards.
The average British soldier from Britain or Ireland was well-trained, well-equipped, and was led by battle-hardened veterans. I wouldn’t call him reluctant or poorly motivated. He was ready to fight.