My voltage was about 13.6 when engine running at 2000 RPM for years.
My batteries would "go bad" after 2 years and i thought I had a drain issue.
Finally I upgraded the big-3 and now I'm seeing 14.2 at the Scanguage and my battery is no longer dead when sitting after a few days.
I think my system wasn't charging properly and the big 3 helped.
Correct again ! A wet 6 cell lead-acid battery needs min. 13.8 volts to charge properly. If it goes over 13.8 by any more than 1 volt, that can also damage a 12 vdc wet cell.
This variance that folks see is normal as long as it's within this "window" of 13.8 to 14.8 vdc.
I just lifted this little tutorial from "Battery School" and it's most informative.
General Battery Care Procedures
Never let the electrolyte level of a wet battery fall below the plates. Lack of maintaining the electrolyte in a wet battery causes damage (sulfation) to the exposed portion of the plate which reduces capacity.
Never store a battery in a discharged state. The sulfate that forms during discharge should not be ignored for an extended time period because severe sulfation will take place sometimes, making the battery impossible to recharge fully.
Sulfation starts at voltages less than 12.4(6.2) and at specific gravity less than 1.225.
Always fill your serviceable, wet batteries with water (preferably distilled)...after they have been charged (provided the plates are covered). If the electrolyte level is at least above the plates, do not fill the battery until after recharge.
The electrolyte expands during charging and if you fill them before recharging, the electrolyte will possibly bubble out of the battery. The plates must be covered with electrolyte for recharge but be careful not to overfill.
Don't use battery strap that locks onto the battery posts for transporting battery. This type of device can physically damage the battery's internal connections.
Don't hammer battery cable clamps down on battery posts. This damages internal parts of the battery.
Don't add acid to a battery low on electrolyte solution. This increases the % acid above acceptable limits and causes pre-mature failure. Add only distilled water.
Don't use a fast charger that increases voltage across the battery terminals above 16 volts, especially when connected to the electrical system of the vehicle. A fast charger can damage sensitive electronic components.
Don't disconnect a battery cable while engine is running. This causes the charging voltage to rise since the voltage regulator loses its reference and cannot regulate the charging voltage. The higher voltage and voltage spikes can damage electronic components.
Always allow batteries to 'cool off' after charging. The cooling time is very important because heat is generated during the recharge and discharge cycles. Without the cooling time the heat grows, accelerating grid corrosion which is one of the major causes of battery failure.
Never charge a wet battery with a sealed (gel cell) battery charger. The wet battery needs the higher voltages to finish the charge and without it the batteries never come back to 100% and sulfation can occur.
Never charge a sealed (gel cell) battery with a wet battery charger. The higher voltages (above 14.8 volts) that a wet battery charger generates cause excessive gassing too fast for the sealed battery to recombine, causing dry-out and battery failure.
Always keep the tops and terminals of batteries clean and free of corrosion. The film on top of the battery can cause the current to migrate between the posts, accelerating self-discharge.
A fully charged battery will give you the best and longest service. Be sure the batteries are fully charged before testing or using in your vehicles.
Even a perfectly new battery that is discharged only will fail load testing. Various states of charge of a battery, without a drain or load, after the surface charge has dissipated, are:
12.66 volts = 100% charged
12.54 volts = 90% charged
12.45 volts = 80% charged
12.39 volts = 75% charged
12.27 volts = 60 % charged
12.18 volts = 50 % charged
11.97 volts = 25 % charged
11.76 volts = completely discharged
In situations where multiple batteries are connected in parallel, series or series1parallel, a replacement battery(s) should be of the same size, age and usage level as the companion.
As batteries age, their maintenance requirements change. Generally their specific gravity is higher. Gassing voltage goes up. This means longer charging time and/or higher finish rate (higher amperage at the end of charge). Usually, older batteries need to be watered more often. And, their capacity decreases.
Inactivity can be harmful to batteries. If they sit for several months, a 'boost' charge should be given; more frequently in warm climate (about once a month) than in cold (every 2-3 months). This is because batteries discharge faster at higher temperatures than at colder temperatures.
Monitoring either stabilized open circuit voltage or specific gravity will tell you when to charge and how much to charge batteries that are being stored.
Battery voltage should not be allowed to drop below 12.4 for 12-volt batteries or 6.2 for 6-volt batteries.
Specific gravity should not be allowed to drop below 1.225."
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