I can only speak from personal experience, our mileages are similar i'm just under 40 miles round trip. I only have a bionx 6.4A/hr battery and i charge at work so in theory i have double the charges you have. I can honestly say that i have noticed no decrease in the battery capacity over the year and fully expect another 3 years out of it. I know different batteries have different quality but they are not that different so i would say the battery has failed under warranty.
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