I replaced a dying battery in my Mazda MPV with a Motorcraft BXT35, and am learning about batteries and charging. Internet wisdom tells me a fully charged car battery reads 12.6 volt as each cell produces 2.1 volt. And a small drop in voltage is quite significant.I have had the Motorcraft battery since Monday, and it seems to rest on 12.45 volt, which is at about 75% charged based on knowledge from internet forums. Wondering whether it's true, or if it is, why, I used a trickle charger to charge up the battery until the charger says it's charged. Right after I disconnect the charger, the battery reads 12.6 volt, and after an hour or so, it settles to 12.5 volt. Please educate me on this, do I have a problem here or i am just plain stupid. thanks.
battery question
- Thread starter windeye
- Start date
- Status
measuring SOC with a voltmeter is crude at best, so be careful of getting too worried based on this method of testing. *Nothing* beats a hydrometer.
Is the battery in the vehicle?
Are there *any* loads on it when you measure (dome light, hood light, etc.).
What is the voltage it reads when it's charging?
How long is it on the trickle charger?
If there is ZERO load on it, and it's at roughly room temp, then it does sound to me like it has aged some. see if you can find and decipher the date code stamped into the carcass.
Is the battery in the vehicle?
Are there *any* loads on it when you measure (dome light, hood light, etc.).
What is the voltage it reads when it's charging?
How long is it on the trickle charger?
If there is ZERO load on it, and it's at roughly room temp, then it does sound to me like it has aged some. see if you can find and decipher the date code stamped into the carcass.
Don't stress yourself. Just charge the battery when driving the vehicle and be done with it.
Life is very short my friend.
Life is very short my friend.
Originally Posted By: meep
measuring SOC with a voltmeter is crude at best, so be careful of getting too worried based on this method of testing. *Nothing* beats a hydrometer.
Is the battery in the vehicle?
Are there *any* loads on it when you measure (dome light, hood light, etc.).
What is the voltage it reads when it's charging?
How long is it on the trickle charger?
If there is ZERO load on it, and it's at roughly room temp, then it does sound to me like it has aged some. see if you can find and decipher the date code stamped into the carcass.
When I measured it, all the light were off, no any other accessories. just the "hidden" current draw, which I did not measure. I'll do it after the state inspection.
And yes the battery is in car, connected, when i measured it.
Car's charging voltage at idle is 14.5. Garage temperature is at about 40 deg F, not at room temperature of 68deg F.
The battery I got from Ford dealership, man. date on it was June 2010.
I tried to measure the battery in my other car, it's a 4 year old OE battery by Panasonic, it was at 12.6.
measuring SOC with a voltmeter is crude at best, so be careful of getting too worried based on this method of testing. *Nothing* beats a hydrometer.
Is the battery in the vehicle?
Are there *any* loads on it when you measure (dome light, hood light, etc.).
What is the voltage it reads when it's charging?
How long is it on the trickle charger?
If there is ZERO load on it, and it's at roughly room temp, then it does sound to me like it has aged some. see if you can find and decipher the date code stamped into the carcass.
When I measured it, all the light were off, no any other accessories. just the "hidden" current draw, which I did not measure. I'll do it after the state inspection.
And yes the battery is in car, connected, when i measured it.
Car's charging voltage at idle is 14.5. Garage temperature is at about 40 deg F, not at room temperature of 68deg F.
The battery I got from Ford dealership, man. date on it was June 2010.
I tried to measure the battery in my other car, it's a 4 year old OE battery by Panasonic, it was at 12.6.
Originally Posted By: casperfun
Don't stress yourself. Just charge the battery when driving the vehicle and be done with it.
Life is very short my friend.
life is in deed too short, can argue on that.
Don't stress yourself. Just charge the battery when driving the vehicle and be done with it.
Life is very short my friend.
life is in deed too short, can argue on that.
This could be a case of the trickle charger not rising to a high enough voltage to squeeze the last 20% into the battery.
Or an inaccurate voltmeter.
Some batteries state 12.8 volts is fully charged, some state 12.6.
Voltage can be an okay indicator of battery state of charge if the battery has not charged or discharged within 12 hours.
It's my opinion you put a trickle charger on a fully charged battery to keep it fully charged. One needs higher amps or a trickle charger than can bring the battery voltage into the mid 14 given enough time to truly fully charge it.
Or an inaccurate voltmeter.
Some batteries state 12.8 volts is fully charged, some state 12.6.
Voltage can be an okay indicator of battery state of charge if the battery has not charged or discharged within 12 hours.
It's my opinion you put a trickle charger on a fully charged battery to keep it fully charged. One needs higher amps or a trickle charger than can bring the battery voltage into the mid 14 given enough time to truly fully charge it.
some times a cheep vom might give readings a little off. this is caused by the vom having higher ohm than a higher quality unit.
Quote:
based on knowledge from internet forums
There's your problem right there.
The resting voltage of a fully charged lead acid battery will vary with the lead alloy used in the battery. Calcium and antimony are commonly alloyed with the lead to achieve low/no maintenance characteristics. The 12.6V is just a nominal value, that can vary by tenths of a volt.
I just replaced the battery in my Subaru. It was made by Johnson Controls. The resting voltage was 12.58. It was on it's last legs and would drop to 9.6-9.8V cranking. The replacement Duralast Gold has a resting voltage of 12.53 and only drops to 10.8-11.0V cranking.
The Motorcraft batteries are among the best.
Ed
based on knowledge from internet forums
There's your problem right there.
The resting voltage of a fully charged lead acid battery will vary with the lead alloy used in the battery. Calcium and antimony are commonly alloyed with the lead to achieve low/no maintenance characteristics. The 12.6V is just a nominal value, that can vary by tenths of a volt.
I just replaced the battery in my Subaru. It was made by Johnson Controls. The resting voltage was 12.58. It was on it's last legs and would drop to 9.6-9.8V cranking. The replacement Duralast Gold has a resting voltage of 12.53 and only drops to 10.8-11.0V cranking.
The Motorcraft batteries are among the best.
Ed
OK, equipment:
1. Charger is a Chicago Electric Power Systems battery charger and starter. It has a 2 amp low rate charging mode, which is the one I used. According to manual, after fully charge the battery the charger automatically switches to float/trickle mode.
2. The VOM I have is a gidital meter, made by Commercial Electric. don't know how to attach an image here, but the meter is not a $10 [censored] meter. I used the 20 Volt range on VDC, which measures 0.01 volt difference.
Back to the charger, i measured the voltage during charging, the highest it made was a little over 14 volt from time to time, most of the time it's between 13.5 to 14.
1. Charger is a Chicago Electric Power Systems battery charger and starter. It has a 2 amp low rate charging mode, which is the one I used. According to manual, after fully charge the battery the charger automatically switches to float/trickle mode.
2. The VOM I have is a gidital meter, made by Commercial Electric. don't know how to attach an image here, but the meter is not a $10 [censored] meter. I used the 20 Volt range on VDC, which measures 0.01 volt difference.
Back to the charger, i measured the voltage during charging, the highest it made was a little over 14 volt from time to time, most of the time it's between 13.5 to 14.
A 2 amp charge is really for small motorcycle batteries. If the charger has a 10 amp feature, use that. It's not gonna hurt it. The amps will taper down as it fills up. Right after engine starting for a short duration, your alternator might be feeding it 30 to 50 amps.
That charger may not have temperature compensation. The lower the temperature, the higher the voltage needs to get to fully charge it.
I have a couple group 27 deep cycle batteries. Crown( the manufacturer) says bulk charge them 20 amps each at 14.5 volts at 68 degs F.
Since starting batteries have higher cranking amps, they can also accept higher charging amperage.
Give that thing some amps and retest.
In my opinion, the old slow trickle charge being best is an old wives tale right in line with the concrete floor draining a battery with a plastic case. It was true when battery cases were made of asphalt, but now the only reason to put it on wood is so the concrete floor does not suck the heat out of the charging battery, or to protect the floor from battery acid.
That charger may not have temperature compensation. The lower the temperature, the higher the voltage needs to get to fully charge it.
I have a couple group 27 deep cycle batteries. Crown( the manufacturer) says bulk charge them 20 amps each at 14.5 volts at 68 degs F.
Since starting batteries have higher cranking amps, they can also accept higher charging amperage.
Give that thing some amps and retest.
In my opinion, the old slow trickle charge being best is an old wives tale right in line with the concrete floor draining a battery with a plastic case. It was true when battery cases were made of asphalt, but now the only reason to put it on wood is so the concrete floor does not suck the heat out of the charging battery, or to protect the floor from battery acid.
Propflux01
$100 Site Donor 2025
IIRC, the optimum no-load voltage for a fully charge battery at 72F is 12.54 Volts.
Originally Posted By: Tim H.
IIRC, the optimum no-load voltage for a fully charge battery at 72F is 12.54 Volts.
Tim, could you shed more light on this as why 12.54 is optimum?
Any correction of voltage due to temperature? thanks.
IIRC, the optimum no-load voltage for a fully charge battery at 72F is 12.54 Volts.
Tim, could you shed more light on this as why 12.54 is optimum?
Any correction of voltage due to temperature? thanks.
Originally Posted By: windeye
Originally Posted By: Tim H.
IIRC, the optimum no-load voltage for a fully charge battery at 72F is 12.54 Volts.
Tim, could you shed more light on this as why 12.54 is optimum?
Any correction of voltage due to temperature? thanks.
OK, I tried 10A charging option, it was only a few minutes till the charger says "charge complete", then the charger cycles, the "charge complete" would light up for a brief moment, and then go off, so on and so forth. The amp would go between low and 10.
When I was using 2A/Auto mode, the charger has the same behavior cycling on and off but at a slower pace. Is this normal behavior for battery chargers?
Originally Posted By: Tim H.
IIRC, the optimum no-load voltage for a fully charge battery at 72F is 12.54 Volts.
Tim, could you shed more light on this as why 12.54 is optimum?
Any correction of voltage due to temperature? thanks.
OK, I tried 10A charging option, it was only a few minutes till the charger says "charge complete", then the charger cycles, the "charge complete" would light up for a brief moment, and then go off, so on and so forth. The amp would go between low and 10.
When I was using 2A/Auto mode, the charger has the same behavior cycling on and off but at a slower pace. Is this normal behavior for battery chargers?
Propflux01
$100 Site Donor 2025
Originally Posted By: windeye
Originally Posted By: Tim H.
IIRC, the optimum no-load voltage for a fully charge battery at 72F is 12.54 Volts.
Tim, could you shed more light on this as why 12.54 is optimum?
Any correction of voltage due to temperature? thanks.
Was taught to me in my Electronics class back in the early 80's, however, this is as close reasoning as I can get:
The following is common for a six-cell automotive lead-acid battery at room temperature:
Quiescent (open-circuit) voltage at full charge: 12.6 V Fully discharged: 11.8 V
Charge with 13.2–14.4 V
Gassing voltage: 14.4 V
Continuous-preservation charge with max. 13.2 V
After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V
Open circuit voltage is measured 12 hours after charging to allow surface charge to dissipate and enable a more accurate reading.
All voltages are at 20 °C, and must be adjusted -0.022V/°C for temperature changes.
http://en.wikipedia.org/wiki/Automotive_battery
Originally Posted By: Tim H.
IIRC, the optimum no-load voltage for a fully charge battery at 72F is 12.54 Volts.
Tim, could you shed more light on this as why 12.54 is optimum?
Any correction of voltage due to temperature? thanks.
Was taught to me in my Electronics class back in the early 80's, however, this is as close reasoning as I can get:
The following is common for a six-cell automotive lead-acid battery at room temperature:
Quiescent (open-circuit) voltage at full charge: 12.6 V Fully discharged: 11.8 V
Charge with 13.2–14.4 V
Gassing voltage: 14.4 V
Continuous-preservation charge with max. 13.2 V
After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V
Open circuit voltage is measured 12 hours after charging to allow surface charge to dissipate and enable a more accurate reading.
All voltages are at 20 °C, and must be adjusted -0.022V/°C for temperature changes.
http://en.wikipedia.org/wiki/Automotive_battery
- Status