Tim,
The engine does not rely upon a good battery to run so you should not be left stranded by a flat battery.
The first thing I would do is measure the voltage at the battery with everything off, and engine not running, then progressively turn lights on and check the voltage. The voltage should start around 12-13v and then drop slightly when you turn things on, if the voltage drops a lot then the battery either need charging or is duff. If charging the battery initially solves the problem, then over a period of time the problem returns then the charging system is failing.