How To Fix Your Power Drain

We've discovered a truth in life. When you have four or more vehicles inyour fleet, your biggest problems become empty gas tanks and deadbatteries. Gas is an easy one; you can siphon it directly from the lawnmower or the neighbor's boat. But what about the battery? Why does itdie, and what kills it? Knowing the answers to these questions will helpyou understand and hopefully prevent a belly-up battery.

The Battery

In simple terms, a battery consists of a lead-coated electrode calledthe anode and a lead-oxide coated electrode called the cathode thatcombine to form a cell. There are six of these cells in a 12-voltbattery, each contributing about 2.1 volts. They are immersed in asolution of sulfuric acid and distilled water called an electrolyte andconnected through a system of grids and plates in a series that ends atthe positive and negative terminals. As the acid eats away at themetals, the cathode releases positively charged ions into theelectrolyte solution. Since it retains the electrons, it becomenegatively charged. Similarly, the anode reacts to the positivelycharged electrolyte and releases electrons and becomes positivelycharged. This movement of electrons creates a polar difference betweenthe oppositely charged plates in each cell and creates a difference orvoltage between the two terminals. When you hook up your battery cables,it creates a circuit and allows electrical current to flow. Simpleenough.

Battery Death

When the French dude Andre Ampere gave us ways to measure this electriccurrent flowing through a wire, the amount of storage capacity in abattery soon became rated in terms of the ampere hour (A.H) using acommon scale, such as the 20-hour rate of discharge. For example, a 100A.H rated battery will discharge below a useable level (10.5 volts) in20 hours with a load of 5 A (5 A x 20 hours = 100 A.H). Obviously, mostbatteries are rated below this, but we used an easy number forillustration purposes. If that 100 A.H battery had a 2.5A draw (like adome light) it would drop below 10.5 volts very quickly (2.5 A x 40hours = 100 A.H).

To perform diagnostics, you'll need more than a voltmeter. You need toobserve the movement of the amp flow, and that requires an amp gauge.The rule of thumb here is to draw the line at the amp load you'rewilling to accept while the car is sitting. You likely won't notice adraw of about 0.15-0.17 A on a car that's driven every day, but if it isa street machine that sits for weeks at a time, you should get the totaldraw down to 0.01 A. According to the Battery Council International,anything above that point indicates a problem that should be fixed.

First the obvious stuff. Headlight doors are notorious for staying onand drawing power, so we checked them and took note of the brake lightsand headlights, and we looked for anything that was humming with thebattery connected. If there is a draw that is more than 10 A, you'llneed to find it before you hook the amp meter up or you'll blow itsfuse.
First the obvious stuff. Headlight doors are notorious for staying onand drawing power, so
We disconnected the negative battery cable to hook the meter in serieswith the entire vehicle electrical system. It doesn't matter which cableyou disconnect, reversing polarity will add a negative to the ampreading but will still indicate the amp draw.
We disconnected the negative battery cable to hook the meter in serieswith the entire vehi

The meter we used has a 10A and a 300mA port and a common ground. Bothof the amp ports have corresponding rated fuses. In a pinch, we've usedautomotive-type glass fuses in the 10A port after popping the one itcame with. See the Buy a Meter sidebar for prices and where to buy.
The meter we used has a 10A and a 300mA port and a common ground. Bothof the amp ports hav