Using battery power to go off the City's power grid

ricevs,

Thanks for the comforting words.  However, the low level components could draw 1 (idle)-100 watts (loud music).  Without the battery charger, after 24 hours the battery would lose 24-2400 watt hours, with a dead battery unable to be recharged.  So it makes sense to run the battery charger all the time when not listening, IF you keep your low level components on.  

There is a question of what strategy preserves battery life the longest.  Suppose the battery has 4000 cycles of life.  If the cycle is prolonged by charging less frequently, then the life is prolonged.  But if the battery is constantly being recharged, the short cycles accumulate fast.  With cars, the alternator constantly recharges the battery, and the battery only lasts a relatively few years.  We are hoping these big batteries in our inverter system last longer than car batteries, so what is the best battery charging strategy?  I think I read that Goal Zero advises letting the battery run down a little, but obviously not to a very low level.

No matter how you use LifePo4 batteries.....they will last at least 10 years......by that time there will be batteries that have 4 times the capacity, last 30 years, weigh practically nothing and cost practically nothing.....anotherwords, find something else to worry about.  JUST DO IT!!!!!!

Good points. I heard that hybrid car battery manufacturers are looking to replace lithium batteries which can overheat with some sort of new "solid state" technology I don’t know much about.

How hot do your friend's dual Amperetime batteries get?

The batteries/BMS can handle 200 amps charging and discharging......He is charging with 40 amps and is discharging at 60 amps max.......so they may rise a degree or so....stop worrying.....JUST DO IT!!!!!

This is not a car.....in a car you need the most watts per lb.(energy density).....so LIthium Ion batteries are used.....however, they are not as safe as Lithium Polymer (LifePo4)......In our homes we use LifePo4 because they are generally safer. What the car industry is looking for is even more energy density and even lighter and more safe.....they will get there.....then we can use these batteries with our inverter.

LifePo4 batteries are already very energy dense......a 200 amp hour AGM battery is typically 125 lbs......A 200 amp hour LIfePo4 battery is 49 lbs.  The AGM battery is less than half the price.....but you cannot use all of its capacity and they only last less than half as long......They will actually cost you more over time and perform less good.  LifePo4 is pretty darn good (for now)

Maybe you will come up with some other concern......My sweet child.....I will hold your hand as we cross the street....You will be safe.

Not sure why you want to be off grid other than during a thunderstorm?

With proper voltage regulation and filtering grid power is fine. Inverters can be noisy too. Especially under quick peak loads.  Much power thermal losses with inverters too.