Here's How:
Locate an old or used UPS that is functioning properly. These are commonly used by people with computers to protect their systems in case of power interruptions, and to filter power dips and spikes. When the battery wears out, most people throw their UPS away because it is obsolete and they cannot obtain a replacement battery, or they may just want to get a more powerful unit.
Check the voltage of the UPS battery to make sure that it is a 12 volt battery.
Check the wattage of the equipment that you want to keep running in the case of a power outage. Check the maximum wattage output rating of the UPS. This is the the most wattage that the UPS will handle in the case of a power outage. The UPS will not handle any more wattage than it is rated for.
Purchase a 12 volt battery. You can usually find a fairly good quality battery on sale for under $50 which will serve your purposes. Generally speaking, the higher the "Cold Cranking Amps" an automotive battery is rated at, the better the battery will serve you. Automotive batteries will work well for fairly low wattage demands and short periods of usage, however a marine quality deep cycle battery will work best for higher wattages and longer periods of time.
Check the connector type on the UPS battery. Most of these connectors are the spade (flat) female type connectors. Purchase 2 connectors which will fit in the connectors from the UPS. If possible, take the old UPS battery with you when you purchase the connectors. This way, you can make sure that you are buying the right connectors.
Purchase 2 metal hose clamps. These will be used to clamp the wires from the UPS to the battery terminals. If the battery you bought has the screw type terminals, you won't need these clamps.
Cut 2 pieces of 12 gauge wire of sufficient length to go from the battery to the UPS.
Measure how much bare wire will be needed for the UPS connector and battery terminals and strip the insulation from the ends of the 2 wires to fit.
Attach the ends of each wire to each of the wire connectors.
Clamp the other ends of the wires to each of the battery terminals. If your 12 volt battery has the screw type terminals, wrap the stripped wire ends around the screws and tighten the screws.
Attach the battery terminal wires to the UPS battery wires. Black is negative, red is positive.
Plug the UPS cord into your 110 volt house outlet.
Turn the UPS on. The UPS should indicate that it is running normally.
Plug a lamp into the UPS "Power Protected" outlet. The light should come on.
Unplug the UPS from the wall outlet. The lamp should stay on. Most UPS units will emit a beep or give some other indication that it is running on the battery and not the house current.
Tips:
Check the UPS wiring diagram to make sure that you are connecting the UPS battery wires to the battery correctly.
A wire stripping tool, such as can be purchased at an auto parts store, works very well for stripping the wire ends and clinching the connectors.
If you have multiple lights on your tank, you can stretch the battery life by plugging only one light and other essential equipment into the "Power Protected" outlet of the UPS. Plug the other light and all other nonessential equipment into the unprotected outlet.
If you have only one protected outlet in your UPS, use a power strip to attach more equipment.
Once your UPS is set up with all of the equipment on and running through it, unplug the UPS from the wall outlet to make sure that everything keeps running as you planned.
What You Need:
UPS
12 volt battery (Marine Deep Cycle battery is preferred)
2 wire connectors
12 gauge wire
Wire stripping and connector clinching tool. (Optional)
