Batteries are Cheap, Backup power is expensive

@joeycastillo  - I lived in California a long time.  The power may not go out but it's not always right... :D 

That's kind of what I'm talking about, but in my case I'm going to leave  the inverter in 24/7.  Inverter is sized at 500W, and I'll use 50W.  Batteries will stay on a charger 24/7.  No transfer times.  At most in an emergency when my Ecoflow isn't working or doing other duties It may draw 110W.  I'm starting off cheap.  I had a 500W inverter for the car/emergencies already. It was $70 or something.  I'm going to try it out for now and see how it goes.  If I win the lottery or something I'll consider something significantly larger. 

By my calculations, with 2x 100Ah batteries I should get about 40 hours of run time for Internet alone.  

@erik_squires 

I now understand how you're planning to wire this setup of yours. I think it will work. Mine is more manual. I use the Inverter when I want to be standalone. Then after nearly draining the battery, I then connect the batteries to a charger to fully charge it back. 

So, in your case, you want 24x7 power from the Inverter. in that case, you need a Charger sized to keep the battery "charge" at the same time feeding your devices.

you need to research how to determine this power rating necessary to accomplish this. or crudely, i will attach an amp meter between the battery and inverter when you have all your devices plug in and determine the amps drawn. then choose charger based on that. (give it some headroom) 

@joeycastillo For the sake of simplicity and cost I think in case of a long term outage I’ll manually enable the inverter.  

I just tried the inverter I already have and it’s a lot noisier than I expected, even at idle.  For now, I think I’ll go with leaving a smart charger on the batteries to keep them topped off and if we ever have a real outage I’ll hook up the inverter as needed. 

Perhaps a future me who is wealthy and can do all the other home upgrades he needs will provide an inverter upgrade. 

@dinov +1 Same here. I think it is a Cumings natural gas generator with 50A/120V = 6kW. For brownouts and the 5–10s between power out to generator auto-on, a few small APS do the job.

OP @erik_squires : Re UPCs, also consider battery degradation. At work I had a couple of Desktop PC-size UPCs (120 and 240V) to protect our scanning electron microscope mainly from brownouts. Batteries need to be replaced every 5-10 years. For one they cost, and in one case the batteries ballooned and I had to cut the case to get the batteries out. Between installation and full failure, the battery performance degrades, so if you really want to make sure your back-up lasts for the desired time, also factor in lowered battery capacity with time, or schedule regular battery swaps.

@oberoniaomnia  - That’s another thing.  The lead-acid batteries used in the common UPS does not have the lifespan of modern  LiFePO4.  

According to Gemini, I can get 5 to 15 years of service vs. 3 to 5 years with lead-acid. 

Generally, APC is still selling designs it came up with it seems 20 years ago while battery technology has really moved forward.  The one good thing is that in the US at least the lead recycling rate is high and environmental contamination low for lead acid.