1st Generation battery won’t hold charge any more

I installed a 1st-generation Ring doorbell in early March 2017, and during the past few months the battery life has decreased dramatically. Now it only holds a charge for 3-4 days. Hard-wiring is currently not an option. I've gone through the recommendations for improving battery life but nothing will extend it noticeably. Since the battery isn't replaceable, what is the expected life span of this product? Does it really only last about 3 1/2 years?