A trick of the light: (charging a 6v battery with a 12v charger)

Miserly charge = 6v misery

I really ought to buy another 6v battery charger. The last one came from the set-aside electricals pile at the tip and, with a couple of resoldered dry joints,  gave many years service maintaining diminutive 6v motorcycle batteries in good health.

The problem, of course, arises out of the number of machines in the garage than any special fault in the battery (though bikes definitely benefit from a 12v system). More than one machine means reduced riding time for them all – I only have so much arse to go around – which, in turn, means that the batteries leak away their charge living in the forlorn hope of a nice run out any day now.

Battery tenders and the like provide a modern solution to the problem but that's to spend money and wait for the postman (or finding a local bike dealer that still sells 'accessories') here we're interested in the situation as described: you have a dead 6v battery and only a 12v charger to hand – cancel the ride or resort to Heath Robinson?

A bulb, a bit of flex from an old domestic iron and your car charger: 6v Heaven

And the latter gets the cigar every time. A solution is dead simple and here's what you need: an automotive bulb rated 12v 5W, a length of wire, a crocodile clip or two (or a bit of electrical tape), soldering iron and solder (or more electrical tape).

The trick is to deploy the 12v charger but drop the voltage reaching the battery such that it receives only what it needs. To do that, you wire the bulb in series with the charger and battery so that it (the bulb) consumes a portion of the migrating electrons thereby reducing the quantity which reaches the battery. Confused? The circuit diagram is your treasure map:

Fag packet or back of an envelope, digital stylee

As with all Heath Robinson contrivances it's probably best to shell out on a proper charger but this will get you going in the meantime.

NB Mondo is not responsible/accountable for your demise while playing with electricity. Play safe.