Is this home-made pesticide from cigarette butts and battery acid safe?
This seems like a bad idea to me.
The use battery acid (sulfuric acid) seems really terrible. In the past there was an awful problem with coal power plants releasing sulfur oxides into the air which formed acid rain (sulfuric acid). You're proposing making a brew that is orders of magnitude worse than acid rain to put on your garden plants. I think such a strong solution of acid would get rid of the bugs by killing your plants. ;-)
If you goggle nicotine &quot;bug spray&quot; you can find a number of websites that discussing seeping tobacco in water, then filtering the brew to make a spray. In such a solution the nicotine is so dilute that it would be safe to handle. However concentrated solutions of nicotine like used for various e-cigarettes could be dangerous to handle. Lookup nicotine MSDS in google (here is one such MSDS sheet).

(1)So no battery acid is needed.
(2) The various websites state that the sprayed nicotine solution decomposes fairly quickly - a couple of days, not weeks.

Frankly I don't smoke or chew tobacco. Since I'd have to buy the tobacco for such a use, I'd rather just buy a commercial pesticide and follow its use instructions. It is absolutely crazy to me that so many folks so berserk when they see the word &quot;chemical.&quot; If you showed a strawberry to most folks they would just identify it as such. But it is nothing but a sack of hundreds of chemicals. So to me all strawberries are &quot;organic strawberries.&quot; To someone who is allergic to strawberries one can be deadly. Did you know that there are varieties of lima beans which have a high enough concentration of cyanide that eating them can kill? (dangerous foods) So spraying a nicotine solution may seem &quot;natural&quot; but it is still a chemical.