Battery charge only reaches 13V
- Thread starter mrtask
- Start date
Gargo
Active Member
Unfortunately it not that simple.... you maybe measuring the charger voltage. 
Not sure about your slow charger, but a modern 'smart' charger will first charge at 14+V for a few hours (or longer), until it sees that the battery is charged. Then it reduces the voltage to a floating charge of ~13v.
If the battery is good or bad and charged with the charger floating at ~13V, as soon as you disconnect the charger and measure the voltage, you'll be measuring the floating voltage not the 'resting' voltage of the battery.
Previously if you were measuring 14.5V, you're measuring the battery voltage soon after the charger was still charging the battery, not the resting voltage.
Best to disconnect the charger and let the battery rest, for a few hours, before taking it's voltage. You can notice the voltage dropping, even on a good battery.
I remember my dad had a rhyme for a battery's charge. "12.7 to heaven, 12.6 bit sick, 12.5 barely alive"
The fact it needed a charge at all, would say to me, you'll be replacing it soon.
Not sure about your slow charger, but a modern 'smart' charger will first charge at 14+V for a few hours (or longer), until it sees that the battery is charged. Then it reduces the voltage to a floating charge of ~13v.
If the battery is good or bad and charged with the charger floating at ~13V, as soon as you disconnect the charger and measure the voltage, you'll be measuring the floating voltage not the 'resting' voltage of the battery.
Previously if you were measuring 14.5V, you're measuring the battery voltage soon after the charger was still charging the battery, not the resting voltage.
Best to disconnect the charger and let the battery rest, for a few hours, before taking it's voltage. You can notice the voltage dropping, even on a good battery.
I remember my dad had a rhyme for a battery's charge. "12.7 to heaven, 12.6 bit sick, 12.5 barely alive"
The fact it needed a charge at all, would say to me, you'll be replacing it soon.
jp928
Well-Known Member
Seeing as the P6s only have an ammeter I occasionally plug a digital voltmeter thing in the cigarette lighter socket to see what the alternator is producing. You should see at least 14.5-14.7 on a just started engine, falling back to 14.1v after some steady miles. note that the cheap digital display units are not very accurate, so it would be good to calibrate one against a good DVM.