6-volt or 12-volt, the Dummy Question

multi-voltage battery charger

If, as you've probably heard before, "A little knowledge is a dangerous thing"; what sort of thing is zero knowledge? Well, readers, today we're going to find out. Someone once asked google, "How to Charge a 12 Volt [sic] Battery on a 6 Volt [sic] Setting." Demand Media scraped up the question and one of their crack contributors attempted to address it at OurPastimes.com. The problem was that Beverley Benham had no idea what she was talking about...

Fortunately for her readers, the question was not the opposite: "How to charge a 6 volt battery on a 12-volt setting." If that had been the question, Benham would probably have killed someone. Beverley's "answer," such as it is, was

"Charging a 12-volt battery using a 6-volt setting is easily possible, but it takes twice the time."

Benham based her answer on her understanding of – get this – Ohm's Law. Yes, Beverley really did introduce her topic by telling her readers that,

"Volts simply represent the pressure of electricity that flows through a cable, and ampere is the unit used to measure the amount of current required to power a device. If you multiply voltage and amperes, you find wattage.".

...after which she blathered for a couple hundred words about how to set up the charger (a "suitable stable work surface") and how to determine whether charging is complete ("If the charge rate is low, your battery is charged.") She got all that from a Brit kiddie site about electricity and a website about the charging system in motor vehicles, neither of which has squat to do with battery chargers!

The real answer, readers, is "You can't." Modern six-volt chargers charge a battery to a maximum of about 7.25 volts, which is still substantially lower than the discharged voltage of a 12-volt battery. That level is around 10 volts, so you could run the charger for days on end and never get the 12-volt battery charged. Sorry, Bev... All of that means that Benham's "B-Tech Certificate in Physics" probably should have been a D-Tech certificate. That, or our Dumbass of the Day should have learned something about batteries instead of pretending to know about electricity. What would really be useful is finding the rubbish she used as a reference...

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