Electrical issues

What problem are you trying to solve? If you measured a drain of 45 milliamps, that is only slightly more than the industry-standard of 35 ma. At that rate, a good, fully-charged battery will be strong enough to crank an engine fast enough to start after sitting for three weeks.

Well, you will have to explain that to the insane engineers who can no longer get anything done without a computer that was never needed before. Every computer has a memory circuit that draws a small standby current. You do not have a real lot of computers in a 1993 model, but consider that a 1999 Cadillac could have up to forty seven computer modules.

To make matters even worse, beginning around the mid 1990's, a lot of vehicles started using body computers and/or engine computers that draw as much as three amps when the ignition switch is turned off, for as much as twenty minutes before they go to "sleep mode". These require a whole new procedure to measure current drain. Simply changing the range the meter is on will wake up the computer, blow the meter's internal fuse, and you will have to start all over.

Unless specified differently by the manufacturer, the industry-standard is 0.035 amps is the maximum allowable "ignition-off-draw", (IOD) current. Chrysler says at that rate, a good, fully-charged battery will be able to start an engine that has been sitting for three weeks. Cadillac is one notable exception. They allow up to 50 milliamps.

Most 1993 models do not get close to 35 milliamps. The biggest drain comes from the radio. It needs the memory circuit to keep the station presets and clock set. A lot of GM radios will display the time for a few seconds when you press the volume knob and the ignition switch is off. I have run into a few where that circuit stays on. If the radio does display the time, it will stay on and will kill the battery in less than three days. If your radio does not have that feature, but the circuit stays on, the only clue will be the excessive current drain goes away when the radio's memory fuse is removed. There may not be a separate fuse for that. The interior lights fuse, cigarette lighter fuse, or horn fuse could be used.

What are your other vehicles? What do you consider "not acceptable"? Is it the amount of current drain you found or do you think no drain is acceptable?

You are absolutely wrong that no drain is acceptable. If that is what you believe, there is a way to stop the IOD that is used when the new vehicles sit in storage for months before being sold to a dealer. They can be started and driven by the delivery driver, but the radio and many accessory systems will not work. Only safety systems must work, like wipers, power windows, and exterior lights, but that might only be when the engine is running.
At first Chrysler products had a bullet connector in the smaller positive battery cable to be unplugged for storage. Later, we had to install a ten-amp fuse in the under-hood fuse box as part of the new-vehicle prep. Current models have two ten-amp fuses inside that sit inside a double yellow holder for easy removal. I do not know what method GM used, but I can guarantee you there is something.

If you think no drain is acceptable, explain how the clock in your radio keeps time when the ignition switch is off. Explain how diagnostic fault codes remain in the engine computer's memory until they are erased by disconnecting the battery. If you do not believe the thousands of mechanics, you will find the information in any service manual.

I stand corrected. Your truck also allows up to 50 milliamps of drain. I tried to copy and paste the page, but the formatting did not copy. The first document is for the spec of 50 milliamps. What follows is the service bulletin copied from an online service manual. I learned the GM does not have a way to stop the ignition-off-draw other than to disconnect the negative battery cable.

Bulletin No: 02-06-03-010A

Date: July 02, 2004

INFORMATION

Subject:
Battery Parasitic Drain
Models:
2005 and Prior Passenger Cars and Trucks
2003-2005 Isuzu Light Duty Trucks
Supercede:

This bulletin is being revised to add the 2004 and 2005 model years. Please discard Corporate Bulletin Number 02-06-03-010 (Section 06 - Engine).

In automotive terms, a parasitic drain is an electrical load that draws current from the battery when the ignition is turned off. Some devices, such as the PCM and the radio memory are intended to draw a very small amount continuously. These draws are measured in milliamps (mA).

In normal use, parasitic drains aren't usually cause for concern, because the battery is replenished each time the vehicle is driven. But, in long-term parking situations, parasitic drains may discharge the battery enough to cause a no-start condition. New vehicles in dealer stock and airport long-term parking are two such situations.

An abnormal parasitic drain could be a glovebox or luggage compartment light that remains on but undetected. Or an electronic component may malfunction and cause a parasitic drain that is larger than normal specification.

Parasitic Drains and On-the-Lot Battery Discharge

Important: In most cases of discharged batteries in low-age, low-mileage vehicles, proper charging procedures with approved charging equipment is the only repair necessary.
Here are some rules of thumb that might help relate parasitic drains to how long a battery would last on a parked vehicle. The Reserve Capacity (RC) rating multiplied by 0.6 gives the approximate available ampere-hours (AH) from full charge to complete rundown. Somewhere between full charge and complete rundown, the battery will reach a point at which it can no longer start the engine, although it may still operate some of the electrical accessories.

Using up about 40% of the total available AH will usually take a fully-charged battery to a no-start condition at moderate temperatures of 25°C (77°F). Put another way, for a typical battery in a storage situation, depleting the available AH by 20 to 30 AH will result in a no-start condition.

Important: If the battery begins storage at 90% of full charge, reduce the available AH accordingly.
The recommendation for maximum parasitic drain is around 30 mA (0.030 amp). A typical drain today actually falls into the 7-12 mA range, even though some vehicles do approach the maximum. Multiply the drain (in amps) by the time (in hours) the battery sits without being recharged. The result is the amount of AH consumed by the parasitic drain. The actual drain may be small, but over time the battery grows steadily weaker.

Here's an example: a vehicle with a 30 mA drain and a fully-charged 70 RC battery will last 23 days. But if that battery is at only 65% of full charge (green dot barely visible), it is going to last only 15 days before causing a no-start.

Effects of Temperature on a Standing Battery

The parasitic drain will be fairly constant over a range of temperatures. The important temperature is that of the vehicle at the time a start is attempted. Colder temperature raises the threshold of a no-start by increasing the residual power needed. When the temperature falls to 0°C (32°F), the battery will be able to put out only about 85% of its normally available starting power, and the engine may need as much as 165% of the usual power to start.

The combined effect of these two factors is to reduce the number of days the battery can stand with a parasitic drain. At 0°C (32°F), the battery can stand only half as long as it could at 25°C (77°F). And at -19°C (0°F), the standing days are reduced to one-fourth.

Temperatures above the moderate climate of 25°C (77°F) increase the battery's internal self discharge. If the battery is in a locale where the temperature is averaging 32°C (90°F), an additional 5% to 10% of the available ampere-hours will be lost in a month due to self-discharge within the battery. At temperatures below the moderate range, self-discharge will be low enough to be negligible compared to the parasitic loss.

What the Policies and Procedures Manual Says About Parasitic Drains

Because determining how long a battery may last in a storage situation is not precise, the P & P manual provides a clear-cut policy, excerpted here.

"Discharged batteries can freeze at temperatures as high as 0°C (32°F), causing permanent damage. Other permanent damage may result from allowing batteries to stand discharged for extended periods."

"To alleviate this condition, the negative battery cable should be disconnected on vehicles which are not going to be in service within a 20 day period, beginning from the time the vehicle is shipped. If this is not possible, batteries should be recharged periodically, every 20-45 days, until the green eye is visible."

"Disconnected batteries will slowly discharge, especially with higher temperatures; therefore, even disconnected batteries should be checked every four months and recharged if necessary."

"Vehicles on display are subject to battery discharge due to drains from courtesy lights and other accessories. Provision to maintain battery state of charge for these vehicles will be necessary."

Consult your P & P manual for full details.

Tracking Down the Source of a Parasitic Load

If the battery in a vehicle becomes discharged in a shorter time than described earlier, the vehicle may have an out-of-specification parasitic load. Refer to Service Information (SI) for procedures for locating parasitic drains. Follow these steps:

1. Build the vehicle.
2. Select the Engine section.
3. Select the Engine Electrical sub-section.
4. Select Diagnostic Information and Procedures.
5. Select Battery Electrical Drain/Parasitic Load Test.
You will need the J 38758 Parasitic Draw Test Switch and a digital multimeter set to the 10A scale.

Important: Read the procedure and follow the steps exactly as described in SI. The following is a summary, not the complete procedure.
The test switch permits you to place an ammeter in series with the battery negative cable. Before performing the test, the engine must be run and all accessories must be operated as instructed. After shutting the ignition off, turn the test switch off. Now, all the current being used by the vehicle is shunted through the ammeter where it is measured. If the reading is out of specification, the procedure explains how to pinpoint the cause.

A Final Word About Battery Testing

Your dealership has an essential tool, the Midtronics Micro 410 Battery Tester, J 42000. Use it to quickly identify batteries that are serviceable and can be charged. Refer to Corporate Bulletin Number 02-06-03-006A for more information about this tool.

Surely. According to that bulletin, your 45 milliamps is higher than what is commonly found, but it is still acceptable, by just a hair. You also mentioned the truck sat for three weeks, which coincidentally is exactly what Chrysler says is the limit for any of their vehicles starting with a fully-charged, good battery. Remember that as batteries age, lead flakes off the plates. That means every day you actually have less battery than the day before. I have a '93 Dodge Dynasty with less than 5,000 miles. Every time I drive it, I have to stick a battery in it, but I have let it sit at times without removing that battery. I did get six weeks out of the original battery when the car was new and sitting on the dealer's lot while I went nuts every night with rustproofing, but now at home, when I stick in an older battery, I only get a week or two before I have to connect a slow charger for an hour to get it started.

If this is going to be a recurring problem for you, consider connecting a small solar-powered maintenance charger that you can set on the dash. Most that I've seen plug into the cigarette lighter socket, but that will only work if your lighter is live all the time and works with the ignition switch off. If the ignition switch has to be on for the lighter to work, it would have to be on for the solar charger to work too. That can't work because the charger would be trying to run all the computers. Instead, look for a tap on the inside fuse box the charger can be connected to. GM used to always have one marked "B" or "B+". That would be the one to use. They also had one marked "IGN". That one is only live when the ignition switch is on and it's not the one you want.