kskane

If the battery is fully charged and giving you 12.4/5v output on standby, then how long can the car sit before the battery will drain to a level where jump start is necessary? I have the old white lead-acid battery on my E60.

Also, how low does the battery has to get to i.e. 1v, or 2v or 10v at which it won't be able to start the car?

BimmerFan52

how long can the car sit before the battery will drain to a level where jump start is necessary? - Too many variables to be able to answer accurately. Age of battery, condition of battery, how much is it charged during each cycle, ambient temperature.

how low does the battery has to get to i.e. 1v, or 2v or 10v at which it won't be able to start the car? - Again too many variables to answer accurately. Condition of engine, ambient temperature, grade of oil (heavier grade of oil requires more energy to turn over engine), condition of starter motor, etc.

kskane

Thanks for the input BimmerFan52, understand the variables highlighted by you (one would hope it is a car and not a human being at times ), but maybe I should have mentioned that under ideal condition, how long will it last before the battery drains to a level where it cannot start the engine. I believe, it is my human curiosity to know my car a bit better since I am trying to do most of the repairs as Indy's and $tealers are unreasonable.

Some contributors from other forums have shared there experience as below;
"100% charged = 12.6 volts
75% charged = 12.4 volts
50% charged = 12.2 volts
25% charged = 12 volts
0% charged = anything less than 11.8 volts
Assuming the battery is holding the charge properly and there are no abnormal parasitic discharges, it should hold for more than 1 or 2 months."

Since it is mentioned 1 or 2 months, that is 100% difference, so I am wondering if that is right, also, is that 1 or 2 months indicating 0v or 11.99v

Or has, there been a person who measured the battery voltage when they needed jump start.

EvolutionVIII

I just did a battery swap in a 525i yesterday. Customer complained about having trouble starting. It was at 12.39 volts with car off and key out of ignition. And barely dropped. After 20 min it was at 12.30 v. I put the key to on position but didn't start and battery instantly dropped to 9. Something volts. I don't know exactly what your looking for but a bad battery would drop instantly once the power is on.

kskane

Thank you EvolutionVIII, so far there is evidence of 9.+v will not start the car. Any more situations like these? I am just trying to figure out how long can I leave the car (assuming it is functioning normal as it is a very sensitive human baby ) so I can start it without jump starting. Is it 1-2-3.....8 weeks time. I am sure a lot of owner's would benefit from this information who don't use there baby everyday.