Hi again...
Totally appreciate that none of the following will help answer your original question, namely tracing the movements of August BARTELS, but for the record here's a summary of the thread I started over on the German equivalent of Rootschat.
Facts first. Guesswork to follow.
1) Both the 1894 and 1896 "Official Directory" of people living in Rostock list a C BARTELS, factory worker
(fabrikarbeiter), and his wife Marianna née
(geb.) PRALOW. They moved there in 1873.
1896 Official Directory
(Officielles Verzeichnis)http://www.rootschat.com/links/0w1p/2) Both the 1900 and 1902 "Directory of Residents" list the widow
(Wwe) of C BARTELS, Blacksmith
(Schmiede) living at 51 Feldstrasse. This is the same address as given in the 1900 census by Frau Anna BARTELS geb PRALOW.
1900 Directory of Residents
(Einwohnerverzeichnis)http://www.rootschat.com/links/0w1n/1900 Census
(Haushaltungslisten) - Image 588 of 891
https://familysearch.org/pal:/MM9.3.1/TH-267-11757-67603-43-----
Guesswork...
- From 1877 onwards several of the annual "Directory of Residents" for Rostock list a Carl BARTELS, assistant blacksmith
(schmiedegeselle) living at various addresses on Feldstrasse. Perhaps this is Carl and Anna/Marianna.
- Possibly "factory worker"
(fabrikarbeiter) could also be translated as a "foundry worker".
- Carl last appears in the 1896 Directory. In 1900 Marianna is listed as a widow. So presumably Carl's death is between 1896 and 1900.
- In 1908 and 1910 the "Directory of Residents" list the widow
"M BARTELS geb PRALOW" and
"Marie BARTELS geb PRALOW" living at 15 Kasernenstrasse and 72 Kasernenstrasse respectively.
The 1912 Directory lists a widow by the name of
"Mirjahne BARTELS" living at 28 Borwinstrasse. Annoyingly there is no
"geb PRALOW". As a widow she seems to have changed address several times so I'm guessing that this Mirjahne is another name for Anna/Marianna/Marie.
1912 Directory of Residents
(Einwohnerverzeichnis)http://www.rootschat.com/links/0w1w/- There is no listing for a widow BARTELS in the 1914 Directory so Anna/Marianna/Marie/Mirjahne may have died, probably between 1912 and 1914.
-----
You can purchase a copy of the record of death for Carl and Marianna from the Rostock City Archives. These records have the potential to be very informative depending, of course, on the informant's knowledge. Unfortunately as you don't know the exact date of death you'll be charged a research fee which will bump the bill up to 50-plus euro.
Having said that, it's free to wander into the City Archives and do your own research. I don't suppose you live anywhere near North-East Germany.
-----
It sort of feels as if this couple are your g-g-grandparents. No real way of knowing though until you start spending money.
Personally I would put the Rostock info on hold until you check out the BARTELS family from Malchow mentioned in the 1867 census. (See reply no.12 earlier in this thread.)
To do that it looks like you'll have to hire the Malchow microfilms through your local LDS Family History Centre. Have you used a FHC before. Happy to advise if you want.
Kirchenbuch, 1698-1888
Evangelische Kirche Malchow
https://familysearch.org/search/catalog/214075-----
A big thank you to Zwobot for taking the time to help out on the German thread

Regards
Beg