Sitting for a month should not cause any problem,
but the battery may be discharged. Measure the battery voltage. It should be 12.5 volts DC.
If lower voltage but still about 12 volts, you can charge the battery with a trickle charger (no more than 1 amp) and it will take about 5 hrs.
If less than 12 volts, take the battery to an auto parts store for testing under load to see if it is any good.
I hope this helps.
