Battery drain rate

95 Honda del sol - charging system appears to be working o.k. - charge rate 14+ volts w/ engine running. Battery never seems to attain a full charge (new battery). Decided to check for battery drain with key off. With Ammeter in series, the battery drain when first connected was in excess of 1 amp (1.45), then after a couple of seconds drain went to about 400 ma. Have never seen this “spike” before when checking this way. Any idea what Honda says the normal “key off” drain should be. Can’t find this information anywhere, but it must exist. HELP!

Popular Mechanics thinks 50 ma with power off is acceptable (not make specific info).

Help with battery drain

Dunno about your car, but typical sleep current is about 50 mA. 400 mA is high but possible.

If you have a 70 amp-hour battery, 0.4 amp should take about 85 hours (3.6 days) to lose half it’s charge.

How do you define “full charge”? Measuring open circuit voltage is very temperature dependent.

I suspect that you have a parasitic drain somewhere. A good independent mechanic can find it or you can start pulling fuses until the battery drain goes to normal. The last parasitic drain that I found was a small trunk light that stayed on when the trunk was closed.

I had the same problem with a Corolla. The battery died if left fo a week. It was drawing 800ma then after about 5 minutes it would drop. The BCM would go into sleep mode. The problem was, if anything was on it would not go into sleep mode of about 40ma. I started pulling fuses and links to get me to the BCM. I found the trunk switch was not turning off the truck light. Once I got that solved the drain was gone. The Toyota Sienna has a AC clutch relay that fails and keeps the BCM on and drains the battery. On new cars everything is computer controlled and it makes it harder to figure out what the problem is. Your Del Sol is older and it should be much easier. If you have an aftermarket radio or alarm, I would pull their fuses first and see what the draw is. If you isolate it down to a fuse we can help with a schematic.

As noted by others, initial drain will be high until computers go to ‘sleep’. After that, somewhere around 50 mA is typical. Aftermarket accessories such as amps and CD changers sometimes stay powered up and increase drain to troublesome levels.

Where are you measuring the 14+ volts? Are you certain that battery cables and grounds have nice shiny clean connections?

Also, though it rarely happens any more. a failed diode in the alternator can cause you to read normal voltage but not do much charging. Is there a hint of a flicker in the charge light in the dash?

You can test things like the trunk light yourself. Remove the bulb and then check the current draw. If it drops to 50 ma or so and it returns to 0.4 amps when you reinstall the bulb, you found the culprit. Then you can isolate the reason, like a faulty switch. It could also be an interior light, or a bulb in the glove box if your car has one.

I had a similar problem with a 1991 Jetta. I had a battery die in the first year, and again 2 years later, and again a year later. Finally decided it was the dome light. It operated on a timer, so it stayed on for a minute or so after you left the car.

Sometimes the timer didn’t work and the light stayed on. if this happened AND I didn’t use the car for a few days, the battery was killed. Never found the light staying on, but once I turned the dome light off, the problem never reoccured.


Easily 10 times too much. Pull fuses one by one to see when the current makes a big drop. Then dig a bit deepr to see what all is hooked to that fuse. Aftermarket alarms and stereos are notorious for big draws like this.

A 400ma draw will drain a battery over a long weekend. You’ve got advice above that should lead you in the right direction.

What do you mean by the battery never seems to attain a full charge? Do you mean the engine has spells of not starting, lights dimming, etc?
Any add-on electronics such a stereo amps and so on?

That much of a parasitic draw could be a problem but I might ask if that high current draw is there several hours after the engine has been shut down?

My Lincolns and the Lincolns my sons owned all have high current draws when first shut off (600-700 Milliamperes) but after some of the electronics go to sleep inside of an hour the draw is more normal.

A quick thing to look for . . .

Do you have any charging devices for GPS or ipod plugged into your cigarette lighter port?

There are some cars out there that have the cigarette lighter hooked up to 30 circuit

Translation . . . you will drain your battery if you leave those devices plugged in after the engine is shut off

400 mA seems quite a bit too high. Even 100 mA would be stretching it. It’s possible the 400 mA reading would go down to 50 mA or less if you waited an hour or two. Try that.

If it stays at 400 mA, all the ideas above are good ones. Especially anything to deal with aftermarket electronic gadgets installed, like stereos and alarms. If you have any of that stuff, disconnect it. If that doesn’t help, if you have a OEM alarm system, that would be my next suspect. See if there’s a way you can disable it.

The only other idea I can come up with … assuming you haven’t been able to isolate the offending circuit by pulling fuses … maybe a shop with a Honda specific scan tool can query the Honda computer to see if there are subsystems powered on that shouldn’t be. On newer cars there are dozens of computers distributed throughout the vehicle, but they tend to communicate with each other over various busses, like the CAN bus. So if you can query those one by one via the CAN bus, you might could get a clue. You’d almost certainly need the Honda specific scan tool for this. Dealership or Honda specialty shop.