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Using an 8V Battery in a 6V Car — Why Not To Do It

September 23, 2010 | Troubleshooting & Repair

By Barry Lee Brisco

A not uncommon complaint in the world of 6 volt 356 owners is that their cars are hard to start. Various "solutions" are proposed, the most common being a conversion to 12 volts, a somewhat costly and time-consuming operation that results in a major departure from stock.

A slightly less high voltage approach is installing an 8 volt battery for just a bit more "oomph" when starting. But this leads to a new set of problems. To charge the 8V battery, your generator will be putting out 9.6V, so you will have to adjust the CO and VR settings in your voltage regulator (if you don't, the battery will discharge rapidly). Since wattage is a function of voltage squared divided by resistance, the 8V battery will be delivering nearly double the wattage (9.6V squared = 92 watts) of the stock 6V battery (7.2V squared = 53 watts).

All the bulbs in your car will be operating at a significantly higher voltage than they were not designed for (ever try to find 8V bulbs?) and they will burn out much more quickly, while 12V bulbs will be too dim.

If you drive much at night, the first bulbs to go are often the headlights. Other electrical components such as relays will also suffer. Those who claim that they are using an 8V battery without any problems probably have corroded grounds throughout their electrical system, creating a higher resistive load and compensating for the increased voltage (remember W = V2 / R, as R increases, W decreases). And then if they don't re-adjust the voltage regulator, the 8V battery is kept in a low state of charge so the electrical components aren't stressed as much as they might be. So with the 8V battery they get slightly better starting (until the battery prematurely discharges) but only because their car has not been properly maintained. They think they've "fixed" their car, but all they've done is put a temporary bandaid on the real problem.

The Right Solution

The better approach is to go through the entire car and thoroughly clean all the grounds (see this article by Tom Farnam that provides a helpful guide to that process). Also ensure that the starter motor is in good working order. That means possibly replacing the starter bushing. Finally, consider installing Joe Leoni's Starter Saving relay kit. It safely delivers a higher voltage to the ignition coil while reducing the voltage that passes through the ignition switch when starting by driving the starter solenoid directly from the battery. This modification is invisible unless you crawl underneath the car with a flashlight, and it prolongs the life of your increasingly rare original ignition switch while improving starting performance.

When new, 6V Porsches started right up, and with proper maintenance they should still do that 50 years later!

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