I know that this is doable, but what I'm wondering is if I can get some help to design some custom circuitry so I can have a stable 12V output to drive a router and a modem (technically this should be a lot more efficient and last longer than the current UPS in place).
This is what I've found so far:
http://www.dansdata.com/diyups.htm
http://www.dansdata.com/upsupgrade.htm
That's given me a basis to work with, now I need to work out how to make it:
-so the voltage to the battery will increase (without affecting the output to the devices) every 3 months for 12 hours (I might be able to use a micro here depending).
-have a smooth transition from AC (I'll use a normal AC-DC converter for this) to battery power (maybe a large capacitor that can handle 15v?)
-turn off when the battery is too low to run the components safely (ADC with the micro?)
-a warning system for when the system is triggered
Any suggestions or links is welcome.
btw, this is the battery I'm looking at using for this build/idea:
http://www.jaycar.com.au/productView...T&SUBCATID=250