Battery Load Test - Batteries Good?
 

Fellas -

2003 Ex with 7.3. Batteries are undetermined vintage; believed to have been replaced by previous owner.

It's been turning over slowly for a few weeks, and this morning turned over especially slow. Had to get the jump box to get it to start. It was fine after that.

Charged and tested the batteries when I got home - both are 13v with no load, 12v with load, and 14v charging at idle. Does this sound right? If so, any thoughts on slow starts and battery drain overnight?

Thanks!

Scott

What kind of load? You need to actually have them load tested, at like 300-500 amps depending on your batteries to actually know their condition.

If batteries check good with load test
Could be bad connections or your starter is getting weak

Loaded at 100 amps - inexpensive tester.

Thanks,

Scott

Connections at the terminal are in good shape.

Truck spun over faster yesterday after I put the charger on the batteries for a while.

Will try testing the starter; I'm not a whiz when it comes to electrical problems, but my battery tester did have instructions on how to check a starter.

Thanks,

Scott

HF has a 500 amp tester for $59 - http://www.harborfreight.com/automotive-...ster-91129.html

Might have to pick up one of these.

Thanks,

Scott

Measure the voltage across the battery while doing a normal start. The voltage should not drop below 10.5 volts dc. A low reading indicates that either the batteries are not providing enough current to the starter, or that the starter is using to much current for a normal start. Try doing a normal start on your truck, shut it off right away and then check for heat at the starter and all of the cables including all of the battery connections with your hand. Heat is an indicator of high current or loose connections.

I have also seen a lot of these trucks with corrosion in the positive battery cables. One truck I've seen had the starter replaced 3 times due to low voltage killing it and the batteries replaced 2 times. I had him crank on it, sure enough, from the positive post on the battery to the positive on the starter, that cable lost almost 3.5 volts. He was down to 7.5v at the starter.

The one thing I have learned in all the battery classes I have taken is that if you need to replace 1 you need to replace both. You always replace batteries in pairs. If you don't the older battery will pull down the newer battery causing it to go bad faster. This is according to John Deere, Exide, Intertstate, etc. I have seen this happen on customers tractors that didn't want to spend the extra for the second battery.

Did not realize that low voltage can kill a starter; good to know.

My terminals are clean; that's one thing that I did learn in the military - always put grease on the terminals after you clean them - keeps corrosion from starting.

Thanks,

Scott

Good info. I'll give it a try.

Thanks,

Scott

Have heard that you should replace both at the same time, but did not know why. Thanks for the explanation.

Scott

The reason you replace both batteries at the same time, is that as the battery ages the internal resistance of the battery changes. The only thing that regulates the level of charge current to each battery is that same resistance. The battery with the lowest resistance will get the recharge current from the alternator and the other battery will not be fully charged. The other dynamic that happens is that the battery with the highest resistance will be drained by the battery with lower resistance as it sits between engine starts.

X100 on what you wrote, you can charge these's batteries and they will crank good for about 24hr's and if no charge is given to them they go dead. Replace both with the most battery you can afford. JMOP

Went to Harbor Freight and picked up the 500 amp battery tester for $60 and loaded the batteries to 400 amps. They had passed the test with a 100 amp tester, but both failed at 400 amps. Starter test was fine - 10v+.

Replaced batteries last night with some the premium Motorcraft batteries, 100 month warranty (3 years free replacement, then pro-rated), 850 CCA. $125 each, but that's not much more than what I would have paid elsewhere.

Old batteries were Autocraft Titanium, 850 CCA. Lasted less than 4 years. Looks like these are the ones sold at Advance Auto Parts.

Thanks,

Scott