Why NOT to use a car battery for your UPS (Power Supply), Its dangerous

** I am sorry for the noise, I am in a server room **

Some videos, including by some who know better are suggesting that the general public could replace the UPS batteries with the much much larger (capacity and weight) car battery, to get a longer run time. This is just dangerous!

1.) Circuit is not designed to charge for days (larger capacity) so cooling will be an issue
2.) Circuit is not designed to work with higher amperage battery (Could blow or short).
3.) Wires are way UNDERRATED. Causing potentials fires.

Its just a bad idea all around.

More Info:

Are there any risks in fitting larger UPS batteries?

Yes. Always the most important factor in any endeavor is safety, from a safety aspect it is important to ensure that the terminals are covered and any external cabling is safe from physical damage.

Second is the risk of overheating and damaging the UPS. While larger units feature ventilation fans to help cool the UPS, smaller UPS often only use heat-sinks and rather small ventilation holes in the UPS housing. When you add larger batteries and the power fails, the UPS will be operating in a heat generating mode for longer than it was designed and if the heat is unable to dissipate the UPS could be damaged. When the UPS is recharging larger batteries, as mentioned previously, the charger will be operating for longer a full capacity and there is a risk that this too may overheat and be damaged.

SOURCE: http://www.apcrbc.com.au/general-ups-information/2-replacing-ups-batteries/11-can-i-put-larger-batteries-in-my-ups