Battery not charging while driving — where to start?

Common one I get on service calls: house battery shows fine at the campsite, but doesn't seem to charge while you're driving. Before you assume a bad battery, check these in order:

1. Is your alternator actually wired to the house bank, or only the chassis battery? A lot of older rigs and DIY conversions never had a proper charge line run.
2. If you do have a DC-DC charger (Victron Orion, Renogy DCC, etc.), check it's getting ignition/engine-run signal — some only activate when they see voltage on a trigger wire, not just because the engine's on.
3. Check the fuse/breaker on that charge line. It's the first thing that trips and the last thing people check.
4. Voltage drop over a long chassis-to-house run is real — if your cable run is 15+ feet, undersized wire will choke the charge current even if everything else is correct.

What's your setup — solar, alternator charging, or both? Happy to help narrow it down.