I think this must be the reason different owners are seeing such a range of battery life results from these very low priced radios; the supplied battery quality is highly variable.
It's not just the batteries supplied with the radios. It's any battery you can buy, an expensive one or a cheap one, a "genuine" battery or one with a fancy brand name.
Mine was fully discharged after 2 ½ hours, backlight off. The
Panasonic battery I purchased after that was hardly better, 3 ½