"normal" current draw when stored?

[kdkrone]

I have been tracing a current leak in my daughter's '93 Acura Legend and it was finally traced to the amplifier after she had destroyed the battery by allowing it to discharge and be jumped, then charged by the alternator. With the amplifier sent off for repair and a new battery, my battery has been losing about 0.04-0.05 volts per day sitting around doing nothing. At that rate, letting it to sit around for 2 weeks would draw it down to 12 volts from 12.6 volts, which is the level from which the new battery started.

That doesn't sound too bad, but if it were my '92 Q45, I could let it sit longer. Does that rate for the Acura seem in the range of "normal" for a car battery?

ThanksKen K

[Q45tech]

Normally a battery discharge rate is reported in milliampere hours not volts, since the voltage drop depends on ambient temperature.

http://www.buchanan1.net/lead_acid.shtml

Due to internal battery leakage most use 1% per day PLUS the parasitic draw against the battery stated rate ~ 80 AH so that's 800 milliampere hours PLUS parasitic [0.050 x 24 =1.2 amperehours] or 2 amperehours per day.

So if one starts with 100% charge [unlikely] it would take 40 days to exhaust a Q battery [brand new unit].........................the question is how much and how quick will the engine require to start.21 days is pushing it depending on ambient start temp and the deviations in temp over the discharge period.

[SteveTheTech]

Ahh parasitic draw tests are one of my favorites. Although measuring available voltage is not really the best way to get an accurate reading of current draw.

Infiniti does not provide a spec for current draw when all the control units are asleep. A typical draw test is performed when the following criteria are met;

Key off All doors locked and the security system armedIf there is a hood switch the switch must be either open or closed (whatever the hood closed position usually is)(Most Infinitis use a Normally Open switch) Connect the multimeter in series (positive lead towards the load)

The measurement is made by using the highest Ampere setting or Autoscaling mode to prevent damage to your internal fuses. Most multimeters use slow burn fuses that are rated to ~10A so having something either wake up or even a door open could blow the fuse so care must be taken.

In most OBD II cars (see my note below) the control units will go to sleep after ~30 minutes and the current draw should drop from a range of 350mA- 1A (depending on model and options)to a consistent reading of <150mA. Now those are standard numbers by any means that is the rough estimate a few of the Nissan engineers and I came up with while at lunch one day.

If the current draw after all the control units are asleep exceeds 150mA then you will need to start removing control circuit protection devices, I usually start with the main audio fuse as it is located under the hood.

Note: I do not know the specifics on the Pre OBDII but the alternator needs to be tested in addition to this procedure. With the increase in age the likelihood of any one of the control units loosing their ability to go to sleep increases, in this case start at the larger circuit protection devices to narrow down the circuit that has a problem. Once you find the problematic circuit reconnect the negative cable and disconnect the suspected component and perform the test again.

This is not a quick procedure and is not for those who do understand a moderate level of electrical diagnostic practice.

[kdkrone]

Thanks for the response. I have found out that the parasitic draw for the Legend is about 40mA (< 50 is acceptable). That being the case, and as , I think, the only easy measurement is the battery voltage, what can I test to tell how much the battery has discharged (percentage? volts?). Not sure how to measure it. Ize just cornfused....

[kdkrone]

I guess the bottom line is --if I have a parasitic draw of, say, 40mA, how long can I let my battery safely sit before I need to start and run the car to charge it up?

[qship96]

Just purchase an inexpensive 2 amp charger, like a Battery Tender Plus, or Battery minder- about $25, and designed for cars in prolonged storage to keep battery at full charge while connected to the car.

most of these are rather small devices and are excellent for garage queens, boats, and other infrequently used batteries that you want to keep from discharging-- NOTE these are NOT battery chargers, they are designed to maintain batteries from discharging due to parasitic loads or even self discharging while unconnected to a load.

[Q45tech]

If you had bothered to read the supplied link, you would have found a battery volt vs ambient temperature chart that correlated with a percentage of battery charge.

Anything below 11.66 volts gets iffy!................again depends on engine compression, oil viscosity, and starter condition.

[kdkrone]

From the website:Temperature: 77 degrees Fahrenheit

Percent Hydrometer Unloaded charge reading voltage 100 1.265 12.63 75 1.210 12.30 50 1.160 12.00 25 1.120 11.76 0 1.100 11.64 It actually seems that below 12.30 is "iffy", not 11.60.

Thanks for the link. I had no idea what a small drop in voltage correlated to.