Off-grid draught beer: we built the battery that runs a tap anywhere

The spot is perfect. A patch of grass by Lake Geneva, shade from a tree, the Savoy Alps showing off across the water. Your friends arrive in an hour, the keg is in the boot, the tap system too. And then comes the sentence we hear at the depot pretty much every Friday: "Er… there's actually no power out there."

The electricity isn't there to push the beer. It's there for the cold. Our taps run on a built-in air compressor, so there's no CO2 bottle to lug around, but above all on a cooling unit that brings the beer down to drinking temperature between keg and tap. And cold costs watts. With no power, you don't have a draught system: you have a tub of warm beer with a tap on it. Nobody wants that. A petrol generator that rattles and stinks, ice that melts every couple of hours: we know the options, and we don't like them.

So we built our own. An old delivery van reached the end of its working life with us, its battery cells were still perfectly healthy, and it turns out we employ people who can't leave things alone. The result: a home-built power bank, 2100 Wh of capacity, 600 W available continuously. Enough to run a professional tap where there is precisely nothing. No socket, no extension lead, no obliging neighbour.

We tested it in a heatwave. No lab figure measured at 18 degrees in a cool depot: we put it through the worst conditions we could find, full sun, cooling unit fighting for its life. Twenty litres poured, and 60% of the charge was still there. In practice, count on 40 to 60 litres depending on the temperature, which is two to three 20-litre kegs. For a birthday, a wedding in the middle of a field or an evening in a mountain hut, that's plenty.

What we won't hide from you: it weighs 20 kilos. This is not your phone charger, it's a serious block to load into the boot and carry to your spot. Bring two arms, or the friend who said "just shout if you need a hand". And keep it in the shade: the hotter it is, the harder the cooling unit pulls, the faster the charge drops.

Where it changes everything. Lakeside, mountain huts, alpine pastures, forest cabins, vineyards, the far end of a garden nobody ever ran a cable to, marquee weddings in open fields. The keg is your usual choice: a Nébuleuse from Renens, a Whitefrontier from Martigny, a BFM from Saignelégier. And if you want sound without a socket either, the portable speaker rents alongside it and runs for twelve hours.

The practical bit: CHF 30 for the same period as the tap (the flat 6-day rental, typically Friday pick-up and Wednesday return), ticked at the "Accessories" step of the booking flow. Everything else is unchanged: free pick-up at our depot on Rue de Genève in Lausanne, delivery on request across the canton, and the usual tap rental at CHF 45 or 65.

So the power grid is off the guest list. It can sulk quietly while we pour pints with our feet in the grass.

— Lupulynn