Here is an update of my Marcus Bates page on www.the27thMaine.com. I've found a little more, but there is still plenty to find.
MARCUS BATES was born circa 1839 [based on age at enlistments] in New Brunswick, Canada. Unknown if he is the 15-year old living with the widow Sybil Bates in Kingston, Kings County, New Brunswick during 1851 census (making a ca 1836 birth year). His death date is not known. On 5 July, 1862, in Houlton, Maine, 23-yr old New Brunswick born Marcus Bates, a ship carpenter, enlisted into the 17th US Infantry for a 3-yr service. The record [US Army Enlistments, 1798-1914] said he had blk eyes, drk hair and was 59" tall (could be an error, that's not even 5 ft). He was discharged for disability on 23 Aug, 1862 from Fort Preble (Portland), Maine. The following month began Maine's 9-month enlistment drive, and Marcus was probably still in Portland when he joined the 27th Maine Infantry Volunteers on 15 Oct, 1862, aged 23. He served until mustering out on 17 July, 1863. Not two weeks later, on 29 July, 1863, 24-yr old Marcus W Bates of Portland, Maine, born in New Brunswick, enlisted as a substitute into the 17th Maine Infantry Regiment. He was a ship carpenter, had dark eyes, drk hair, drk complexion, and had a height of 5'5". On 6 May, 1864, he was wounded in the side during the Battle of the Wilderness. On 4 June, 1865, he and other recruits whose term of service was not yet completed were transferred into the First Maine Heavy Artillery [Red Diamond Regiment, pg 294]. His whereabouts after this time have not yet been found.