Re: Battery Condition

After keeping my car in storage for 3 months, I decided to check on battery status. It was anywhere from dead to drained!
I put a slow charge on overnight, and to my knowledge it is now fully charged. My concern is as follows: With battery fully charged, I put a OHM meter
to it and get a reading of 13.55. As I keep the meter on it, I see the numbers drop about a tenth of a digit every 3 seconds. It dropped to 12.60 in a matter
of about 2 minutes. Is this normal, or is it loosing its charge?

Thank you

When a battery sits on a conventional charger for a while, it tends to sliightly over charge and get warm. Either the over charge or the fact that the battery is warm will change its voltage output slightly upwards. Charged and at ambient temps, it should be around 12.5-13V. You should also know that batteries hate"deep discharging", and that they often begin to sprial downwards after it happens. I'd suggest getting the battery load tested, it is a 15 second proceedure that will "go/no go" confirm your battery's condition.

“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein

Thank you JFP. Good information I will do a load test as soon as I get a chance. For the time being I purchased a battery maintainer and will avoid discharge. I also noticed that at the present time, about 24 hrs later, my multimeter gives me a steady reading of 12.50. Does not seem to be draining as it was when fully charged to 13+. short of having the load test done, I assume it is looking good for now.

while the 1st test numbers came in ok the 2nd test after letting the battery sit a while failed the batter.

Or skip the testing and just replace the battery. While it may not bad yet, it will never recover fully from the discharge. I don't know about you but I can't put up with a going bad battery.

Sincerely,

MarcW.

Car batteries are not designed to be completely discharged, they are designed to provide short bursts of high energy (e.g. to start an engine), they have relatively thin (compared to deep cycle batteries) plates and a high plate count to provide high current for short time intervals.

As a battery ages (and is repeatedly discharged and charged, e.g., by starting and running your car) it goes through a process called sulfation, the lead in the battery sulfate is converted (a little at a time) to a stable crystalline form that no longer dissolves on recharging ultimately reducing battery capacity to the point where it will not crank your engine over. A complete discharge of any lead acid battery will result in some breakdown (sulfation) of the plates in the battery and reduce its life; because the plates are thinner in car batteries a complete discharge will reduce battery life or completely kill a battery a few years old. Sulfation also increases the internal resistance of a battery reducing charge efficiency and increases the rate of battery decline.

After charging your battery you should expect it’s voltage to drop to 12.7 to 12.6 volts fairly quickly since this is the normal open circuit (load) output voltage on a fully charged lead acid battery. Under no load conditions it should hold close to that voltage (within 0.1 volts) for 24 hours. An open circuit battery voltage of between 12.2 to 12.3 volts indicates 50% charge. At 12.0 volts I consider a lead acid battery to be dead! (Note to check the no load voltage on your batter you need to disconnect it from your car.)

Personally if your battery is 3 years or older and has been completely discharged I would replace it. It is simply a dead battery waiting to happen.

Have Fun in your Pcar - Martin