There is very little maintenance to be performed on a well-designed solar electric battery charging system. Solar panels have no moving parts that wear out, they don’t consume fuel and there are no filters to replace.  All you have to do is clean them occasionally with a non-abrasive cleaner and make sure the mounts and fasteners are tight. Vibration, expansion and contraction from temperature changes, can loosen the mounting hardware.

Modern charge controllers also use solid state electronics with no moving parts. Charge controller maintenance consists of checking the wire connections once a year to make sure they are clean and secure. A loose connection causes resistance and heat, both of which are detrimental to system performance.

If you have flooded batteries (which you should really consider upgrading) you should check the battery water level at least quarterly (preferably monthly) and add only pure, distilled water when necessary. The batteries and the wire connections made on or near the batteries is where most of the maintenance is required. Flooded batteries emit gas that contains tiny amounts of the sulfuric acid from the electrolyte.  When this acidic mist lands on battery terminals it causes corrosion.  Inspect the wire connections and clean away any corrosion you find. Clean the terminals and make sure all connections at the battery are snug.  This unpleasant task is unnecessary if you are using Lifeline AGM Batteries or maintenance free lithium batteries.