I've left my '05 HAH parked for a month. The next time I got back in it, the hybrid battery meter was still in the same place, and the car started without any problems. And I live in a hot climate area. Batteries routinely die around here. Sometimes only after a year or two. The heat really stresses them. But so far, I haven't had any problems with my HAH.

Perhaps, your battery was just a weak battery to begin with? It happens. I wouldn't blame Honda. Nor Panasonic. But, I'd keep an eye on it. It might be on it's way out. Take it to an AutoZone and they'll test it for free to see if it has any bad/weak cells.

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