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From an indian perspective, I'd like something like this to replace the lead-acid batteries we use currently in home UPS system. Lithium ones are too costly right now, and if they can make this cheaper and longer lasting than the gel or lead-acid batteries currently in use, they will have a huge market in India.

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I doubt this will be dramatically cheaper than lithium. Lithium itself is fairly cheap considering how little of it a battery has.

Basic LFP batteries can be made pretty much in a garage, both cells, and chemicals for cathode/anode.

Most LFP cells were actually made exactly like that 10-8 years ago. People mixing cathodes, and anodes on a bucket, somebody smothering them on foil, and then somebody doing winding, packing, welding, and, finally, sealing all by hand.

I would have thought that by now LFP has mostly overtaken FLA for home use. I can pick up LFP cells for just over $100/kWh, which is about what it costs me to get FLAs, but with far longer lifespan.

Got a link to where I could pick up those LFP cells for just over $100/kWh?

Head over to diysolarforum.com and look for the group buy thread (it's not really a group buy anymore, it's ongoing). I picked up four 280Ah cells for right at $400 (exact amount varies a bit on shipping destination). Rumor has it that shipping has gotten pretty slow in the last few months, however, so you have to be patient.

Anyway, that gives you 3.36kW of capacity (assuming a 12V 4S config) for $119/kW. To be fair, it will be slightly more when you price in your BMS of choice.

Be sure to invest in a cheap spot-welder to put on charging tabs. Soldering to the ends of batteries is very dangerous. (Even if you see people saying they do it without obvious trouble. Key is "obvious".)

LFPs are usually packaged ready to use with screw terminals, so no welding needed. You just need to connect them with bus bars in your desired configuration.

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