Because while making the Lead Acid Battery you will need to open the Battery, cut the welds, make new battery terminals, melt the Lead, Make new welds for making the series connections, you may also need to check the electrolyte and so on. You will need these metal dies for making the Positive and GND plates terminals.
To make a lead acid cell requires a glass or plastic container, lead roofing sheet that's unused but no longer shiny, 4M sulphuric acid, deionised water, petroleum jelly (eg vaseline) and some plastic to hold the lead plates in place. A hygrometer is used to achieve correct acid concentration.
Harvesting from scrap lead acid batteries is a gamble, as any slight ionic contamination discharges the cells, making them useless. If you're determined to do it, make a test cell using a couple of little bits of lead, charge it in the prospective acid, and test its self discharge time.
Lead acid batteries are a simple technology, and have changed little since the 1800s. Battery banks for offgrid use are expensive, making home made battery banks an attractive option.
Purchase the one as per your requirement. Metal die 1 is used for the large Lead Acid batteries while the metal die 2 is used for the medium size Lead Acid Batteries. This is a 12V spot welding tool and is used for connecting the battery cells in series. This uses Graphite Carbon Rods.
Add water to the Sulfuric acid; be very careful while making the electrolyte for the battery, after adding the water wait at least 30 minutes, so that the electrolyte can get cool. Finally, you can use the Hydrometer to check the specific gravity of the electrolyte.