What I haven't seen much of is this: SIZE MATTERS! Not for voltage, that will remain constant, all else remaining the same, but size DOES affect AMPERAGE! More plate surface area, (and electrolyte) equal more amps, all else remaining the same. So, the 'bigger' the battery, assuming the identical construction, compared to a smaller battery, will have the ability to provide more AMPS, and for long term use, AMPS matter.
Suppose on were using an inverter with 90% efficiency, (Unlikely, but for the sake of argument) And a battery with 100 amp hours available. Now, build a BIG battery, giving 10 times the amperage... It's obvious, that the bigger one can run the same inverter for as much as 10 times as long at the same voltage and amperage... All else considered the same. (It won't be, but that's another story)
As for a container of concrete, I agree, bad idea. Not unless you line it, with either an acid resistant plastic or glass, siliconed in place. My own idea to make a 'recycled battery' is to start with cheap and readily available fish tanks, ten gallon sizes are plentiful and cheap. Taking 'dead' (shorted cell) batteries apart, I can salvage all the good plates, and silicone in glass separators, or partitions, for making cells. I'm less concerned with the precise surface area available, as I have access to many many old lead acid batteries, and I can just add in another fish tank.
Paralleling them adds to the amps, while the voltage should remain pretty constant. I also plan to use a type of perforated plastic for my separators between plates, it's easy to get, cheap, and acid resistant. And it is already full of holes. Cut to size with simple scissors.
Tie the tops of plates together by soldering them together, and leave plenty of empty room at the bottom of the tank for cast off... The stuff that caused the shorted cell in the first place. I know I won't get optimal efficiency, or near best cycling... as these will be already partially spent plates. But, I have a LOT of them, to make up for that. I have the room.
And access to every other component I would need. Except one: Either a solar panel or wind turbine large enough, or even a combination of them, to keep the cells charged and topped of for when I really need them. I could use a generator... Which would be a good idea once in a while anyway, but I'd like to have a set it and forget system... Until the grid goes down, which it does around here. (Tornado alley)
My inverters, which are NO where NEAR 90% effecient, came to me cheap... Old UPS units that were tossed out because the gel cells in them died. I also have several of the so called Modified sine wave inverters meant for automotive use... And i know from experience, that do NOT run anything with a motor in them very well. The motor runs slow, and gets hot. Motors really REALLY want to 'see' a true sine waveform, not a choppy stepped wave, modified from a square wave. Some things don't mind, incandescent bulbs, for example, but who would be using those in a power critical situation? NOT ME!
A better solution, in my opinion, is a HUGE one to one transformer. Like the isolation transformers we used to use working on TVs and such. I believe that will somewhat smooth out the modified sine wave output of the inverters, albeit, with even more losses. The losses, I believe, would be made up for by increased efficiency. Or, close to it.
My idea for this transformer is one of two ideas... Either, back to back microwave oven transformers, (only the 120 Volt sides, the high voltage windings will be removed), and/or, a service garage type battery charger transformer, using the 12 volt coils back to back, two identical units, or as close to identical as i can manage. Their HUGE wires would limit losses due to resistance.
The plus with microwave transformers is, they are so plentiful. Especially during spring cleanup. It's almost NEVER the transformer that makes them go bad and people throw them away.... In fact, I find most DO work. The people just wanted a newer or nicer one. Either way, it's unlikely the transformer is bad, and a quick check with a decent ohm meter will tell the tale in a matter of seconds. It's either good or it's not. (Usually) I built my first welder using microwave transformers, and have rewound many for specialized applications many times, including, heavy duty (for the home) car battery chargers.
So, I'm still gathering 'dead' batteries, and it's not hard to tell if it's just a shorted or 'dead' cell that killed it. Swelled sides will tell me too., what to look out for. In my case, I will not be trying to fit the plates as physically close as possible, just as close as PRACTICABLE. I loose a bit, I know, but, with say, 4 to 8 fish tanks... I really won't care. For the 24 volt applications, I double them up, parallel and serial, and for 12 volt applications, parallel connections.
WATTS are WATTS, either way. No way around it, which is a good thing here. 12 volts at 100 amps still only equal 1200 watts total. Assuming you can only realistically use half of total capacity, (Good practice if you want your batteries to last very long) then, that's only 600 watts. TOTAL. over time, we call it watt hours, and the slower you discharge the more you can take. Discharge at high rates, and the battery will go flat much faster.
Most batteries you see advertised, have a little disclaimer somewhere, saying that the rated capacity is only at something like a 20 hour rate. Not very realistic most times. That means, they artificially raise the apparent rating by a huge factor, when in fact, that 100 amp battery is really only a 50 amp or so. The 10 hour rate is more or less the standard.
And do not forget the square root of 2, rounded to 1.4.... That's what you have to put back in to replace what you took out. Roughly. If you take a 100 amps out, you need to use 140 amps to return it to a state of full charge. This is not counting a float charge, to protect against self discharge. That's in addition, not part of, the 140%.
Anyone have any experience using ANY means of making cheap inverters, or even not cheap UPS units, provide something closer to a true sine wave? Will transformers work, and if I do that, will I loose more than I gain? What are the gotchas in this?
I know I can use digital, aka, switching power supplies with no problems, but anything like a FAN... is a no go. I've tried it. My best luck came from using 12 volt DC fans. (In summer, when it's muggy as all heck, as it ALWAYS is when the storms knock the power out)
I have a generator, but it uses something like 12 gals of gasoline at less than half output, and MUST run at 3600 RAM even at NO load, meaning, it SUCKS the gasoline. Which is hard to get when there's no power for three days. Storing enough for a week long outage, ( the longest we've had in recent years) is both very expensive, and unsafe.
I'd rather switch to propane if I were going to do that. At least, it's rather safer than gasoline, and doesn't go stale... Having to rotate that amount of gasoline every two to three months is seriously expensive. and a pain the... neck. Also, theft becomes an issue when I'm the only kid on the block with any gas... But no one steals propane... Not the big household sized tanks. I do happen to have a 500 gal propane tank out back.
The Scarecrow said that: 10-7 and out.