Why would you upgrade an ups?
If you use 100w-250W on an small ups with an 7Ah battery you might get 3-5 minutes out of it when the power fails and after 1-2 years you need to change the batter which costs half of what a new ups costs of the same caliber, so with other words batteries are way too expensive and the cheap ones won't even last a year.
So with an upgrade it will extend the battery life and extend the running time to one hour if not more depending on the load, don't forget to put the ups in front of an fan to keep it cool because these small upses are not made to run for more than 5-10 min.
Battery & Cables?
Here is a list of everything i used:
- Old 420W ups from phasak
- Old 80Ah car battery
- 2 Car battery terminals
- 2 4mm wires with 50cm
Open up the old ups that was not working correctly even with a low load the ups would shutdown almost instantly meaning the battery was close to dead, make two small holes in the side or back of the ups and extend the black and red wires from where the battery was connected and close the ups back up.
Now get yourself an old car battery that's still works in my case 80Ah car battery and screw the 2 battery terminals onto it, connect the extended wires, red first and black second and test the ups before putting it in it's resting place.
P.S. if your load is higher than 25% the ups will get hotter and you might need to put an internal fan that turn on when the power fails, this way you wont melt the ups or possibly cause an fire.