Homemade lemon-permanganate battery for days when there is no electricity in the grid, but you need to charge a mobile phone and want light to read a book. You need permanganate (from drugstore, common disinfectant), sodium hydroxide (sewage cleaning liquid), sulfuric acid (from old lead-acid battery), aluminum wire, and inert electrode, such as graphite, carbon fiber rod (from an old drone), or nickel wire. This battery gives 3-times higher voltage and 10-times higher current density than a usual lemon-zinc-copper battery.
Can you beat my experiment - it gives a world record cell voltage for a homemade battery (except Li-ion or other non-aqueous batteries that cannot be made at home). Note that a single element with pure Al wire gives upto 3.25 V, when 5 are connected in series, it would give 16V. Household aluminum from the kitchen can be also used, also zinc or magnesium. Prototypes with glass frit or clay membrane (made from bathroom clay plate or clay dish) have longer lifetime and can light bunch of white LEDs for a few days.
Video by Tavo Romann, (C) 2017 Superaccu OÜ.
Check also other homemade battery constructions