SUA2200RM2U -- Replace Battery LED still on after replaced.

I have one at work that I don't think is working. It's been powered off for ages and I just put in new batteries (with the wiring correct I hope...) and it's still flashing a red replace battery light.

I'm hoping that by monday it'll be fully charged and the self-test will pass. If not what should I do?

Edit: It works! EEK! Just had to wait for the batteries to be charged -- apparently they've been sitting there for 3+ years.