If the battery has been dead for a long time it may not be taking a charge. You can try removing it and putting it on a dedicated battery recovery charger.
Autozone will check it out for free (I think).
If it needs to be replaced (I think it will), get a Deep Discharge battery and stay away from a car battery.
Car batteries are designed to give up their charge in a burst (for starting) and don't last long supplying constant current.
TIP: if it says CCA on it run away. Cold Cranking Amps is a "Car Starting Power" measure. Look for words like "Reserve Capacity (RC)" or "Amp Hours (AH)" to denote a Deep Discharge battery. Good 12 Volt ones have capacities from 75AH to 220AH.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW