Only posting this in case some one else has a ups that has an old battery in it and have not replaced the battery. - I guess I could say I experienced a good thing. - I was at my desk when my screens blinked and the UPS alarm wouldn't stop it's continual sound. The backup kept power going. I didn't have a power failure. The price of a battery replacement is 1/2 the price of a new one. Since the ups is 7 years old, makes "cents" to get a new one as all the varistors and other surge thingy's are probably less than stellar by now. I was fortunate cause the battery was really hot, but no fire or explosion. No failures while I was on a trip or something. I was able to remove the battery and place it outside the house on some rocks until I find the proper way to dispose of it. - My ups was an APC model BE550G using a RBC battery. NOt sure what CS3 or LT/206 means, but it was on the battery. - I have used it as a backup to my pc that has it's battery removed and never had a hickup in power so the capacitor inside the ups did it's job on switch over. Especially since the ups waveforms is NOT sinusoidal. It has a total harmonic distortion of 45% and a max single harmonic of 35%. This is common (and sloppy) but they work ok like that. My home alarm system was on the system as well and works fine with it. It has it's own battery to smooth out the system from a non-sinusoidal waveform. I also have a Samsung desktop thin screen TV on it and it plays good as well. Even the Raspberry pi worked ok with it. - I've never had my other APC ups systems die on my before like this. They usually got to where the backup time of power shortened considerably. This failure raises a concern of possible fire if left in place while on vacation. I don't know, but just feel uneasy with this type of failure.