Sorry, this is getting a bit off-topic.
No, I don't use lead acid batteries. I use different batteries for different builds. Lithium ion and lithium polymer (polymer pouch cells are cheaper and better density but I only use them for temp controlled installs) along with lithium iron phosphate for people who want the best long term solutions(also becoming best overall anyway). They have all the expected safety features as well.
As far as lifetime the oldest installs are only ~5 years old. No issues but I wouldn't say it's been long enough to say what the performance really is compared to powerwall 2's claims(don't forget the original "powerwall" was pretty poor and hard not to beat). Compared to initial specs, and 5 year performance they're outperforming powerwall 2 in initial cost, and kWh/$ and they're on track for that to continue barring any failures. What Tesla has is a fancy package(the work is contracted out) where I use cabinets which can be painted any color. At this point I haven't built or installed one in about a year but the only thing that has changed is prices have gone down.
So you reduce costs by sourcing your own cells, building your own packs (and BMS systems?), using off-the-shelf cabinets and providing your own labour?
Let me estimate the costs of that compared to a Tesla Powerwall at 7000/14=500 $US/kWh and tell me if I'm making any errors.
For small qty. commercial or DIY initial cost for cells alone is at best 300 $US/kWh (most are closer to 400 $US/kWh) though I've seen some questionable looking Chinese import cells as low as ~200 $US/kWh. For assembled packs including BMS:
a quality USA domestic assembled pack costs 740 $US/kWh but
"known" quality Chinese are 400 $US/kWh. In a best case you've got 200 $US/kWh saving compared to the full cost of a powerwall but more likely you have only 100 $US/kWh and if you really want an "expensive" option you'll be losing 240 $/kWh already. So
with 14 kWh of cells alone you have at best $US 2800 to come up with BMS, 5kW inverter and enclosure. If you're using pouch cells you need to have additional mechanical components for clamping the pouches properly.
Edit2:
Salvaged/Surplus/2nd hand cells are another option which can go down to ~100 $US/kWh but are very subject to availability and have added risks with warranties, liabilities and some extent safety depending on the source.
Cheapest "known" 5kW (pure sine) inverter on Amazon is $US 550 (I've had issues testing an inverter from this brand in a prototype system),
a "cheap" made in China inverter from a US company is $US1299 and
a quality 5kVA inverter is $US 2540 So with the inverter included you're now $US 1500 left for the rest of the system or nearly completely out if you want to go with the high-end solution.
Other components are relatively low cost: ~$US200 for the cabinet, ~$US150 BMS and then a bit extra for cables, fuses, connectors etc.
Best case, you'd be saving $US 1000 on a $US 7000 component and you're putting together your own using low-tier, made-in-china parts, at cost, with your own labour free instead of buying a complete, ready-to-go, made in the US system with a 10yr warranty and commercial support. Its not even like you can't just buy the Powerwall as a component and install it yourself (at least in Australia)
https://www.ecoelectric.com.au/shop/tesla-powerwall-tesla-14kwh-battery.htmlEdit: All of the listed inverters apart from the last $US 2540 Victron don't have chargers, grid-tie or standards certifications like the Powerwall.
A made in Taiwan, UL listed, 6kW inverter charger from a US company costs $US 2011 but still doesn't have grid tie. That'd make it $US 500 saving best case but should really be more like losing $200 if actually comparing to the functionally equivalent Victron that does grid-tie and charging.
Yea, even with an inverter the cost is less. I've already built backup systems for people before. Even after paying me they paid less for more.[...]
I'd
really like to know what you're doing to achieve that.