Shouldn't be a problem. My company used to use small gel cells all the time as backup power for small electronic systems. If there was out gassing from the battery it would more likely come from being over-charged than discharged.
I assume by small appliances you are talking about things like cell phones, tablets...etc. Motorcycle batteries aren't made for long term discharge so I would only use it for something that doesn't bring the voltage down too much. Try it out and let us know how it works for you,
JJ
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