You cacan try and find a DC auto transfer switch. They use them for solar panel installs and similar stuff. Super expensive for what you are doing, but the only option I know of. It would also require a battery pack for backup. Several series lipos. A UPS really is your best bet. If it is 1W of DC, that's like .1W AC and a decent UPS should last several hours with such a small load.
I did a comparison test of all my air pumps using a kill-a-watt type of a device and found that
10 gallon rated air pump used 1.5 W
20 gallon rated air pump used 2.5 W
USB air pump used 1.5W
I assume there is a .5W overhead for the device itself.
The overhead of the UPS cheap inverter is surprisingly large and will drain a UPS during a power outage even with no devices connected.
I believe running a DC device off a DC battery is more efficient than running having a DC battery convert AC power.
My experience with UPS has been a few hours of air pump not days despite having such a low power draw . Have your experiences been difference?
One option I was considering was connecting a larger lead acid battery or even a small car battery to my UPS.
My end result I am looking for is to keep the air pump going during a power outage for as long as possible so if a power outage outage occurred while I was not home, the fish would still be able to survive.
Usually USB battery banks have a port for charging and a port for the device itís charging. Connect the charging port to an USB power adapter thatís plugged into a timer thatís plugged into a receptacle outlet. The timer is used to charge the USB battery bank a limited amount of time per day and to prevent the battery bank from being charged continuously. Connect the USB battery bank output port to the air pump and youíre good to go. Select a large enough USB battery bank to provide power ride through for the longest outage plus say 24 hours.
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Interesting idea. In this situation, would the air pump be running 24/7 or only when the charging the battery bank is turned off?
My understanding with those battery banks is they are unable to be charged and used at the same time. Its either one or another.
I don't know if plugging in a device to use power will disable its ability to be charged or not. If so, it would require some kind of transfer switch if not, it would then require a balancing act to match the charging to the power draw as to not slowly discharge the batteries. This requires additional experimentation.
Thank you for the idea.