I have the rechargeable variant of the Philips Golite, which looks like the same model that Costco sells. I like it overall, but the big problem I have with it

I have the rechargeable variant of the Philips Golite, which looks like the same model that Costco sells. I like it overall, but the big problem I have with it is that the battery doesn't hold a charge if you keep it in its case for any longer than about a week.