How do I calculate how long it would take for a car battery to drain (to a level that would effect starting) based on an additional parasitic drain?
For example,
If I leave an accessory plugged in that has a power consumption of 100mA while the car is off and sitting, about how long would it take before the battery is dead, or too weak to start the car?
First determine the AH (Ampere Hour) capacity.
Divide AH by parasitic drain in Amps to get Hours of battery life.
The tricky part is knowing jsut when the battery will no longer start the car. There are variables within and without the battery that affect this. To know the answer for your car and your battery would require trial and error.
And, tricky as well is the amount of decrease in total AH the battery will sustain from each time that it is discharged below half.
Tris
So, if I understand correctly:
A draw of 100mA would take 50 hours to drain 5 AH. Since it would seem that even most cheap batteries have 30 AH capacity, you could really have this parasitic drain going for 2 full days without much of a problem starting the car.
This question basically arose as I wondered if leaving my my cell phone or pda charging for a few hours with the car of (cigarette lighter stays on with car off) was draining my battery. Then I wondered about a gps reciever, as I use one with my PDA sometimes, but often find myself in a situation in which I would like to quickly load up the nav software, but the cold start time of the gps combined with being in a moving car took a few minutes to get a fix. But, if I just leave the gps running (blue tooth reiciever) all the time and plugged in to the car, it will always be ready to go, and I don’t have to worry about killing a battery
There are solar panels available which connect to your car battery, and continuously recharge it. You might look into adding one of those.
Of course, the panel would have to produce more charge than your GPS/cell was using, and you’d have to have your car parked somewhere in sunlight.