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.
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.
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 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 hav
Buy a Meter
You'll need an amp meter that can measure at least 0-10A DC to performthese tests. Most multimeters can do this, and you can spend as much oras little as you want to get one. We checked Harbor Freight and found anAC/DC meter made by Cen Tec that can measure up to 20 A of DC currentwith overload protection for $19.99. We also found a Wavetek for $169.95and a Fluke meter for $209 that does the same thing but has a lifetimewarranty. If we had to buy a new one, we'd go with as much meter as wecould afford--the new models have temperature probes and other goodies.The Fluke we used in this story was purchased in 1989 for $85 and itstill works great, so you get what you pay for.
We connected the amp meter and opened the car door to turn on the domelight and got a 2.37
When we closed the door, we found that there was a 0.43A drain occurringsomewhere in the s
The meat of this job was pulling fuses one at a time until the amp meterread 0.01 A. We pu
Amp Hour vs. Reserve Capacity
Even though Amp-Hour (A.H) and Reserve Capacity (RC) are very similar inmathematics and general theory, they have subtle differences. For thepurpose of this article, we used A.H rating to show the rate a batterywill discharge with a small amp draw for a fixed period of time, likewhen your street machine is in storage. The RC rating is the number ofminutes a battery will last if your charging system fails while you'redriving your car. Temperature is a factor, but generally, the RC ratingassumes a 25-amp draw to run essential accessories and the A.H ratinggives you a formula to illustrate what would happen with a smaller ampdraw over a longer time period. Since RC is a more practicalapplication, it is more commonly seen as part of the battery rating.
This car has a newer stereo with a detachable face and a memory so wewere going to call it
Eventually we found that the interior lights were still drawing0.047-0.050 A for a small p