Tracing a French regiment of the line

Hello

I was wondering if someome could help me trace the French regiment of the line (86th) during the Napoleonic wars.

An ancestor of mine enlisted in the 86th (around 1804) and was held captive after the battle of Salamanca (1812). In the records of the Birtish prison (Portsmouth castle) he was still part of the 86 untill the end of the war.

Now I would like to now what the 86th did in the meantime (before the battle of Salamanca).

What battles did they fought as well ?

Was a regiment always kept together ? Or is it possibele that the regiment was split up for different battles at other parts of Europe ?

For example, how did new recruits (in my ancestors' case around 1804) join their regiment (86th) if this regiment was already fihgting miles away at some part of Europe ?

Boris