you dont need a hydrometer to set the specific gravity (SG) - you only need a scales (tarazoo/tarazee/kaanta) to do that. And you need a proper measurement vessel like a container with known good markings to mix the acid in the correct ratio - and finally basic common sense to not pour water on acid and not pour hot acid into the battery and not to drink the acid etc.. (I need to say all these precautions as its 2022)
Once you prep/activate a fresh battery and boost charge it before fitting it in, you will get the best possible service life from it. I used to get 5 years at minimum from such batteries.
btw you also need to make sure your battery is correctly insulated, even mehrans have a plastic shield infront of their battery which people throw away, You can make the insulation blanket with an old puffer jacket or even jute/compressed cotton/rockwool padding.
