Battery Voltage

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Jul 13, 2010 | 08:39 PM

caere

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Battery Voltage

I just had my head gaskets re-done at the local ford. I picked up the truck yesterday evening and it drove fine. THis morning it wouldn't start. The dealer said prob low batteries and to try a boost. A boost worked but I also took the time to clean the battery terminals and test the batteries. THe one on the passsenger side was about 10 V before the boost and the other was about 12.5 V. Once the truck was running I checked the Voltage on the battery terminals again and it was about 13.2-13.3 volts. I recently had to redo the FICM. Should I be concerned about the voltage? Should I upgrade my alternator or do some other change? Where should I be testing the actual voltage when running? I read that lower than 13.5 is not good.

Jul 13, 2010 | 08:50 PM

c473

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One dead battery will cause the charging voltage to be low (<13.2). Service/charge the batteries first. Check for voltage drop (>0.1 volt) on your cables and check for solid grounds. They should both read at least 12.5 after charging over night and removing the surface charge (light load for 10 seconds, headlights should do it). Make sure you test the voltage while they are disconnected. If they both read around 12.5 volts, crank it over while watching your meter, if it drops below 11 volts you probably have a bad battery (the glow plugs can pull them down for about 30 to 45 seconds even after the light goes out). Or, take it to one of the parts houses and have them do a battery/charging system check. They should only be replaced in pairs, if one is bad, it's probably been bad for awhile and the "good" one has been taking up the slack and may not last much longer. With two new batteries you should be seeing around 13.6 volts while running. Low voltage can cause all sorts of problems for the computers.

Jul 13, 2010 | 08:52 PM

solaratomic

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I would be concerned about your battery voltage. Defenately sounds like it's time for a set (Be sure to buy two). As far as the alternator, I would put a set of batteries in it and recheck. You have to keep in mind the alternator was attempting to charge what seems to be a bad battery. You're always gonna show low voltage when this is the case. Also wait at least 2 minutes after cranking to check the running voltage, during the first two minutes the glowplugs are still operating and you won't get a "true" measurement.

Jul 13, 2010 | 09:03 PM

caere

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From: Canada

So the voltage while running is tested on the battery terminals?

If one battery is reading 12.5V with no load or not started can I just do one, I know it's recommended to do 2 but curious if the one seems ok why not just get the exact same make model?

Is the low voltage only due to the batteries and putting in two new ones is gonna get the 13.6V no other repairs needed?

Jul 13, 2010 | 09:10 PM

c473

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The internal resistance of the batteries needs to be matched. Using an old battery with a new battery (mismatched internal resistance) will have you back in the same spot quickly. New batteries that are fully charged will only need light charging from the alternator and you will see the voltage near 13.6 with a good alternator. Last time I checked, two new bats from Ford cost about $230.
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Jul 13, 2010 | 09:11 PM

caere

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$230 US that's not bad.

Can I use a 2Amp trickle charger on the batteries while they are connected in the truck?

Jul 14, 2010 | 11:06 PM

caere

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BUMP

Ok I have driving with the batteries for a bit now and they are both sitting at 12.54 V without the truck started. While started they both sit at 13.35 V. I'm not sure where to measure the voltage while running though?

SO:

Can I just use the voltmeter on the battery terminals? Or is there somewhere else I should be checking it from?

Are new batteries pretty much gonna guarantee 13.6 V or better?