UPS Powers Off During Self Test

I have a SMT3000RM2U APC UPS.  The battery was replaced two years ago.  We do not usually have significant power outages at the location where it is protecting the equipment.  We have noticed lately that when it does a self-test cycle the system powers off and then comes on.  Of course this cycles the power of the devices connected to it.  Is this behavior more indicitive of bad/failing battery pack or more the electronics.  I want to make sure I'm do the right thing replace the battery versus replace the entire unit.