what drained the batteries? charging them will get it running again, but what drained the batteries? your problem: how long was it sitting unused, unconnected? all new batteries - what kind of batteries? lead acid, gel, lithium,...6 or 12 volt,...?
was the engine battery connected? was the use / store switch in use position?
something caused them to drain. batteries, except lithium, drained to empty, zero, damage the battery. if you leave the use / store switch in the use position at least the propane detector will be on. the radio may draw too, from the engine battery, depending on what radio. these components will take a long time to drain battery, but they will given enough time.
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