battery goes dead after sitting 4 days

[wvragtop]

96 cobra battery goes dead after about 4 days sitting .took my meter and pulled the neg post checked milliamp draw and when I pulled fuse #8 it dropped from 110ma to around 40 ma .fuse #8 is chime for keys/courtesy lamp/engine compartment lamp/glove box lamp/power mirriors/instrument cluster/MCM? not sure what this is /trunk lamp/and anti theft (door open sig) cant find any obvious problems like bulbs staying on and such.

 

[SVTCOBRA9629]

Have some one move the plastic key ring on the ignition switch while u have the meter hooked and see if you get a voltage change. Really sounds like u have a cat mouse game ahead if you.

 

[wvragtop]

How many milliamps is normal I wonder

 

[SVTCOBRA9629]

I have no idea, but can check mine for a comparison

 

[xblitzkriegx]

under 50ma is what youre looking for, generally speaking.

 

[wvragtop]

im going to check it again tomorrow

 

[mwolson]

Have you had the battery load tested?

It's kind of hard to find the Ah spec for car batteries, but I found one that is probably fairly typical: http://www.optimabatteries.com/en-u...atteries-8020-164-35-redtop-starting-battery/

That battery has 44Ah. At a current draw of 110mA, that battery should last for 400 hours, more than 15 days.

 

[jeason15]

You can't use the ah rating of a battery as a hard and fast measurement of how long it will last with a current draw. In a perfect environment, the current draw/time/discharge rate would be very linear. However, batteries do not live in a perfect world. You also assume that a battery that is not fully discharged should be able to carry the load of the typical vehicles electronic suite. This is also a misconception. Point is, a 110mA parasitic load will very easily discharge a battery to a useless state in about 3-4 days.

 

[mwolson]

Good to know.

 

[SID297]

You can't use the ah rating of a battery as a hard and fast measurement of how long it will last with a current draw. In a perfect environment, the current draw/time/discharge rate would be very linear. However, batteries do not live in a perfect world. You also assume that a battery that is not fully discharged should be able to carry the load of the typical vehicles electronic suite. This is also a misconception. Point is, a 110mA parasitic load will very easily discharge a battery to a useless state in about 3-4 days.

This. You'd be surprised how little draw it takes over time.

 

[1996MysticSnake]

Do you have a speedcal wired in?

 

[aaron97]

Subscribed...

I'll be going on the same hunt when I get home in May. My '97 does the same, it will kill the battery in just a day or two.

Sadly, its been this way for 10 years. But I have been working overseas for so many years, that I just let it go and buy a new battery anytime I feel like driving it when home on vacation. But I have recently decided to do a full restoration and it starts with finding and fixing whatever is draining the battery. Years ago, when this started, I had loaned to the car to a close friend in need for the year, he took it to a Ford dealer in Phoenix and they said they couldn't find the problem but "suspect its in the keyless entry system". So good luck, ill be watching to see what you find.

 

[CzchMex]

A 100mA draw or less is fine for a daily driven car. More than that is too much. I had the same problem with mine but would take a couple months before my brand new optima battery would be dead. However the moment your battery drops below 75% it becomes deep cycled and will never charge back 100% if not a "deep cycle" battery. So every time it dies it is shortened in life.

I tested everything and found it to be the anti theft system pulling my draw. If I unplugged the PATs from the rear trunk the draw would drop to almost nothing. Unfortunately that is needed for starting. So after killing 3 batteries over the course of a year (never drive my cobra) I invested in a battery tender. Best investment yet.

If you don't want that the. Simply locate the fuse that's causing this (#8 like you said) and add a switch. If the car sits for a while switch it off.

However your battery will never be the same after it dies so it will always get worse.