It's no surprise that the batteries are spotty, and probably won't last long. $16 is a reasonable price for 4 16550 cells, putting those 4 cells in a pack with protection and throwing in a light and charger for $16, well, the cells are not exactly going to be Panasonics or anything.
FWIW my 4 year old Magicshine got 3 hours on a charge.
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Work: the 8 hours that separates bike rides.