What’s more frustrating than hopping in your car, turning the key, and nothing?  You try again, but still nothing.  Nada, zero, zilch! You’ve fallen victim to a dead battery.  There are only a few things that can cause this to happen.  First, the condition of the battery. Maybe the battery is old.  Maybe you don’t drive that car very often, so it sits in storage for long periods of time.  A battery’s internal plates can sulfate and go bad.  Even with normal use, sulfation occurs.  But when a battery is left sitting unused, the sulfate can harden. And when this occurs, the battery will appear to take a charge, but it will not actually hold it.  You’ll want to recharge your battery on a slow setting to try to bring it back up to a full charge, and to see how it reacts.  A good battery will generally read between 13.6 and 14.6 volts at rest.  Once completely charged, you’ll want to do a draw test to see how the battery reacts.  If the battery drops below 9-10 volts on a heavy draw, and then stays below the level it was at before you performed the test, there’s a good chance that you need a new battery.  Generally, if a battery is about 4 years old and keeps going dead, it’s a safe bet that the battery has outlived its usefulness.  In colder climates, this can happen almost overnight in the fall or winter.  Cranking amps of a battery begin to diminish as the electrons move more slowly in the cold, and you can actually get a break in the internal cells of the battery.  If this happens, it’s time to for a new battery.

Another thing that can cause a dead battery is a heavy draw when the battery is at rest.  This can discharge a battery almost overnight. The first thing you should do is recharge the battery slowly.  It is always best to remove the negative cable, and then charge the battery either in or out of the vehicle.  After the battery has been charged to the proper level, but prior to reconnecting the negative cable, take a test light and connect one end to the battery’s negative terminal and the other end to the negative cable.  If the test light lights up, there’s a draw on the system.  The brighter the test light lights up, the heavier the draw.  If it lights dimly, it can usually be attributed to a clock or a radio, which cause a small draw on the battery.  These will drain the battery, but it will take time.  If you use the car enough, there’s no need to worry.  If not, use a small trickle charger when you’re not driving the car to maintain the battery.

Now, if you get a bright light, this is an indication of a draw heavy enough to quickly kill your battery.  Locating the source of the draw is easier than most people think.  With the test light still hooked up between the negative battery terminal and the negative cable.  Start removing fuses one at a time.  A heavy draw generally comes from a “battery circuit” or one that is hot all the time (things like a lighter, courtesy lamps, stop lamps, dome lamp, etc.) even with the car off or with the key out.  When the light goes off, you’ve found the offending circuit.  Once you find the problem circuit, see what is connected to that circuit and start unplugging those items/accessories one at a time.  Again, when the light goes out, you’ve found the issue.  Now make the necessary repairs!

If you have pulled all the fuses and the light continues to stay on, this tells you that the problem is being caused by a “battery unfused circuit.”  Things like an alternator, voltage regulator, headlight switch, ignition switch, and even some accessory ports/lighters will be on an unfused circuit.  Once again, start unhooking these items one at a time being careful not to ground them out (being unfused, these leads and will cause quite a mess if grounded out).  Internally regulated alternators, while usually a great product, are notorious for developing an open diode inside of them that can divert 12 volts to ground and drain a battery overnight.  They’ll charge a battery, operate perfectly, and give you no indication of any problem.  Disconnecting the alternator and having the test lamp go out finds this problem for you.

Always be careful, and very methodical when chasing electrical gremlins.  One step at a time and one connection at a time will keep the frustration level to a minimum.

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With over 40 years of combined restoration experience, Capp’s Hot Rods rebuilds and restores Model As, Deuces, ’33s and up, classic cars of all makes and models, and muscle cars.  Located in Woodland Hills, California, Capp’s specializes in complete wiring services, from repairs to complete harness installations.  Visit their website or call 818-974-7530 for more information, or to schedule an appointment for your classic car.  You can also find the Capp’s team at the Pomona Swap Meet on Road 22, Spaces 22, 24 and 26.