You can find old battlefields just about anywhere here. But there's nothing notable in the vast majority, if anything you'll see some ruins of trenches or fortifications, or a small museum in place if the battle was famous. Only recent and very large battles have big monuments in some places, some of the famous battles of the wars of the modern european mad conquerors, from Napoleon to Hitler.
If you're interested in military history I advise instead visits to national military museums. Some military academies also have museums open to the public. And if you interest is more about medieval or ancient battles seek events with reenactments, those usually happen in summer and may be done in some of the old battlefields. But with the coronavirus running amok don't expect any to be done this year or the next. You'll have to search nearer the date of your visit, and in the regions you intend to visit.