doesn't last

We purchased a pair of lights which seemed to work well for a while. After maybe a month later we noticed that one would be off when we reached our destination. It would flash for about a minute and then turn off. Recharging the light did not help. The other one did the same another couple months later. This is unacceptable and unsafe since I depend on the tail light to stay on to alert cars and other cyclists when it is dark.

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