Car batterys

[Bitsyncmaster]

I decided to put my D battery on the charger (I use adjustable power supply). I set the voltage to get a few amps flowing and when the current stops dropping over time, I know the battery has fully charged. Well my D battery seemed to need a higher voltage to see the charge current not drop to zero amps. I used about 0.2 amps holding on the fully charged battery to read the voltage.

12/28/2016
My D battery charged at 14.5 volts shows 0.12 amps. at 46 deg

1/1/2017
My test battery charged at 13.0 volts shows 0.20 amps. at 70 deg.

1/1/2017
Impala battery charged at 13.3 volts shows 0.20 amps. at 45 deg.

1/3/2017
Malibu battery charged at 12.9 volts shows 0.17 amps. at 47 deg.

I've always had an interest in making an automatic battery charger so I like recording this kind of data. All these batteries are standard lead acid and the Malibu is the only one without the removable battery caps. I know the sealed types (gell and AGM) are a little different for charging voltage. Also the battery temperature affects voltage.

So now the question is....My D battery is either very good or going bad. There is a lot of info on lead acid batteries on the internet but it's very contradictory.

[David T]

Lead-acid batteries suffer from "sulphation" over time. Simply put, you lose surface area of the electrodes over time and charging cycles. Unlike a sponge a battery slowly loses capacity. Also the electrolyte evaporates over time exposing less and less to the electrodes. A typical lifetime for an automotive battery in regular use is about 5 years. Chronic over or under charging will quickly shorten it's life. They are also sensitive to temperature and vibration. IMHO it isn't worth re-inventing the wheel. A Battery Tender is only around $40 and they seem to be very reliable. Be careful with any chargers, exposure to alternating current will destroy a battery so AC leakage must be avoided. AC leakage can also cause electrolytic corrosion showing up first in the cooling system melting the aluminum. Most auto stores will test car batteries for free. They charge them up and load test them to try to determine capacity and compare against the specifications of the battery. When the CCA (Cold Cranking Amps) is less than 80% of the spec the battery is considered bad. Often when you have a car that has a run of bad batteries it means the voltage regulator is bad (over or under-charging) or a diode has shorted feeding the battery AC. Most places, if they are any good, will also check the alternator when testing the battery and vice versa. They live together in a symbiotic relationship. One can affect the other.