I buy batteries off of Amazon (like a lot of people) and keep spares on hand because (just like everything else) batteries can be off specs even on day one. As far as the clicking goes there can be many reasons it is happening, but there are things that you may want to do that you are not already doing that would improve the life of any future UPS that you buy. First, you can buy a surge protecting and power conditioner power strip, or buy them as series devices. I buy Furman for this and usually I will have a 6-plug surge protector (Furman SS6B) at every outlet. My house is already prepared with line conditioning like a lot of people, but I also add a power conditioner (Furman M-8X2) at every station (my main desk uses two). If your house sees a lot of discontinuity, or variation then it will drive your UPS nuts and prematurely age electronics all the way down the pipe.
This is not the end of the story, however. You will have to replace the surge protectors occasionally. I think the $25 is an expense I can live with for the protection it offers to my electronics. Here in lower Alabama/North Florida we get a LOT of lightning. Maybe where you live it is not so bad, but surge protectors are not perfect and they do have a limited lifetime. That's part of the price for protection. If you get a strike local to your house, or experience something like a blown transformer it is a pretty good indication that something may have come down the wire, so just be aware of things and maintain things regularly and you'll be fine.
