So apparently the wiring in my home is... questionable. Very rarely, plugging or unplugging things will cause a power dip. This is almost always the result of turning on a fan or something, is only for a moment before coming back, but its long enough to cause my printer to reset. I want to add a backup battery supply using either the 12v cell pulled out of an old apc ups (before the suggestion of just plugging it into that... I did, somethings fried in it and it will ALSO power cycle everything connected to it every few hours) or an old car battery. Is there any reason I shouldn't use this circuit, which was originally intended for amateur radio equipment?
Also is there anything else i should be considering?
This circuit is correct as it does the job (provides a charge and switch-over when needed).
The only drawback could be that you need to ensure that the battery is sealed as during the charging process the electlorit will slowly evaporate and decrease battery capacity.
I am personally using a UPC as that gives me more options to power-up more stuff including 240V heater and it has a self-test built-in (it is APC1500VA).