Warship lights
If you like to show how a common batleship would look in open sea you should not show ANY light in the portholes but the navigation lights.
Eventually, a signal lamp on one of the wings (bridge level) could flash a preprogrammed message. I am not sure if at that times, they used the topmast flashing lights visible on the 360º. Most probably yes. And I am not sure if Morse code was in force among Germans.
A seaman myself I know what SOLAS convention requires for common vessels but could try to find out the lights used by German warships in WWII times. My brother, a quite qualified modelist could help here.
He dedicated years building models from several Kriegsmarine's units. He builds them piece by piece. He has also collected an incredible amount of information about them.
Some of the extra lights for warships are those signaling current condition (whether she was sailing along or forming part of a group), the level or the highest officer on board and so on. Quite specific, really.
If you like to be picky: there is a light (of blue color) that basically nobody should see except the steering man (at the bridge) located on the centerline, helping him to identify in the dark where the bow was. Anyway, in certain conditions, steering men where not in the bridge but somewhere inside in much lower decks so unable to see outside. Course was kept watching a repeater of the compass in front of them a receiving orders from the bridge several decks above them.
Probably you know this, and sorry for telling you the basics: all vessels, in night time, show few and specific lights, except passenger vessels, fisshing boats and special ones like tenders or trawlers when carrying out their specific function.
I like the idea of charging a battery during the day to show those few lights in nightime.
Sorry for being wordy but hope this contributes to a better model. If not, forget all the above and enjoy!!