I wouldn't bother unless my battery was barely able to make the trip. And then I'd probably just upgrade the onboard battery. Which is exactly what I did with my old Honda Civic. I had two oversized batteries in it and never had any issues, even driving around all day.
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2000 Honda Insight
2000 Honda Insight
2000 Honda Insight
2006 Honda Insight (parts car)
1988 Honda CRXFi
1994 Geo Metro
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