We have a car in the family which does not get very much use. It's my son's who is off to college. We drive it maybe once every two weeks. It's a 2007 Saab 9-5. The battery which is an Auto Zone Platinum is less than a year old. The battery seems to drain if no one uses the car. I have a trickle charger, which also tells you what percentage the charge is. If no one drives the car very much, this battery will drain down on its own to 50%. Is this normal? I use the trickle charger and get it back up to 100% but was wondering. I realize it should be losing something, but 50%?
How much does a normal battery drain if not used
- Thread starter PeterGreen
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Battery's self discharge varies greatly, and increases as batteries age.
the Saab has some sort of parasitic load from engine computer, door lock fob, ect.
The % displayed by any battery charger is entirely voltage based, and is at best a guess, and not to be takes as truth.
A healthy flooded battery can self discharge 12 to 15% per month at an average 75F ambient. Self discharge increases with battery temperature, decreases with decreasing temperature.
Once they self discharge below 80% the battery capacity starts shrinking faster never to be returned.
A trickle charger on a battery slowly depleted to 50% via parasitic and self discharge is an absolute joke. it has virtually no chance of returning the battery to 100% charged, despite that soothing green light it flashes at you. The battery needs to be brought upto 14.4v for a while, and most trickle chargers will never do this, but the word trickle is apparently very soothing to the human ear as it is repeated so often regarding batteries.
the Saab has some sort of parasitic load from engine computer, door lock fob, ect.
The % displayed by any battery charger is entirely voltage based, and is at best a guess, and not to be takes as truth.
A healthy flooded battery can self discharge 12 to 15% per month at an average 75F ambient. Self discharge increases with battery temperature, decreases with decreasing temperature.
Once they self discharge below 80% the battery capacity starts shrinking faster never to be returned.
A trickle charger on a battery slowly depleted to 50% via parasitic and self discharge is an absolute joke. it has virtually no chance of returning the battery to 100% charged, despite that soothing green light it flashes at you. The battery needs to be brought upto 14.4v for a while, and most trickle chargers will never do this, but the word trickle is apparently very soothing to the human ear as it is repeated so often regarding batteries.
How are you measuring 100% and 50%?
I have one car here that will drain the battery to 35% remaining (according to the charger %) in a month even with a new battery, another will go the whole winter and is still able to start the car.
The difference is in the factory alarm, one car arms the system even if the door is locked with the key, the other one will only arm with the remote door lock button. If the one that goes the whole winter is locked by remote the battery will be dead in a short time.
The difference is in the factory alarm, one car arms the system even if the door is locked with the key, the other one will only arm with the remote door lock button. If the one that goes the whole winter is locked by remote the battery will be dead in a short time.
JHZR2
Staff member
Originally Posted By: wrcsixeight
Battery's self discharge varies greatly, and increases as batteries age.
the Saab has some sort of parasitic load from engine computer, door lock fob, ect.
The % displayed by any battery charger is entirely voltage based, and is at best a guess, and not to be takes as truth.
A healthy flooded battery can self discharge 12 to 15% per month at an average 75F ambient. Self discharge increases with battery temperature, decreases with decreasing temperature.
Once they self discharge below 80% the battery capacity starts shrinking faster never to be returned.
A trickle charger on a battery slowly depleted to 50% via parasitic and self discharge is an absolute joke. it has virtually no chance of returning the battery to 100% charged, despite that soothing green light it flashes at you. The battery needs to be brought upto 14.4v for a while, and most trickle chargers will never do this, but the word trickle is apparently very soothing to the human ear as it is repeated so often regarding batteries.
+1 to all this.
Alternators do not fully and properly charge batteries to begin with. Dumb trickle chargers will never allow a balancing charge and proper float. Smart ones with temperature compensation can, but still may be conservative in their logic.
AGM batteries self-discharge slower than regular flooded batteries, so if you are seeing this sort of depletion, I think higher than normal parasitics should also be looked into.
Battery's self discharge varies greatly, and increases as batteries age.
the Saab has some sort of parasitic load from engine computer, door lock fob, ect.
The % displayed by any battery charger is entirely voltage based, and is at best a guess, and not to be takes as truth.
A healthy flooded battery can self discharge 12 to 15% per month at an average 75F ambient. Self discharge increases with battery temperature, decreases with decreasing temperature.
Once they self discharge below 80% the battery capacity starts shrinking faster never to be returned.
A trickle charger on a battery slowly depleted to 50% via parasitic and self discharge is an absolute joke. it has virtually no chance of returning the battery to 100% charged, despite that soothing green light it flashes at you. The battery needs to be brought upto 14.4v for a while, and most trickle chargers will never do this, but the word trickle is apparently very soothing to the human ear as it is repeated so often regarding batteries.
+1 to all this.
Alternators do not fully and properly charge batteries to begin with. Dumb trickle chargers will never allow a balancing charge and proper float. Smart ones with temperature compensation can, but still may be conservative in their logic.
AGM batteries self-discharge slower than regular flooded batteries, so if you are seeing this sort of depletion, I think higher than normal parasitics should also be looked into.
Are you talking voltage drop or some type of charge rate indication and how long does this 50% drop take ??
If you have an issue check the residual draw after the engine is turned off by removing a battery post (Or use a current clamp) and checking how many miliamps the burglar alarm, clock and central locking are using.
If you have an issue check the residual draw after the engine is turned off by removing a battery post (Or use a current clamp) and checking how many miliamps the burglar alarm, clock and central locking are using.
I'm using a Schumacher fully automatic battery charger, model SC-1200A
thanks to all for the helpful replies. am considering getting a better charger.
Originally Posted By: PeterGreen
am considering getting a better charger.
How does this solve your problem? It seems like your car is draining the battery quickly due to parasitic load, and you are charging it every couple of weeks instead of leaving the charger connected 24/7. Your charger has an automatic float mode; it's designed to be left on 24/7
am considering getting a better charger.
How does this solve your problem? It seems like your car is draining the battery quickly due to parasitic load, and you are charging it every couple of weeks instead of leaving the charger connected 24/7. Your charger has an automatic float mode; it's designed to be left on 24/7
If you are looking for a better caliber brand or charger, look to CTEK or NOCO, these are ultra smart chargers that can desulfate and perform other functions to help extend the life of the battery. Many high end car owners leave these types of chargers on continually for off season use with no ill effects.
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