Phone chargers could soon become a thing of the past, after researchers in the UK proved it’s actually possible to keep a smartphone battery fully charged simply by emptying one’s bladder. Though the idea that urine can be used to generate power had previously been established, this is the first time that researchers have managed to harness enough energy to power a smartphone using the volume of pee produced from just one trip to the bathroom.

Charging the battery to its full capacity from zero actually required 4.2 liters of urine (1.1 gallons), which is considerably more than a single person could ever generate when relieving themselves (though an elephant might be able to have a decent stab at it). However, describing their achievement in the journal Applied Energy, the study authors reveal that they were able to keep a Samsung Galaxy juiced up with enough power to make three hours of phone calls for every six hours of charge time, using just 600 milliliters of urine.

To achieve this, the researchers used microbial fuel cells (MFCs), which harnesses the energy produced by certain microorganisms during anaerobic respiration to create a flow of electrons between two electrodes, known as a cathode and an anode. Urine enters the equation as a source of ammonium, which these microbes require in order to respire.

By stacking six MFCs on top of each other, the team were able to amplify the voltage and current produced during this process, resulting in a greater energy yield than had ever been achieved before.

In their study, the authors write that they hope to one day see their technique used to help people charge their phones when caught short in remote locations, where access to electricity is limited.