hope this helps someone.. on a small road trip to ME this weekend 250 miles... noticed the volt gauge going south.. this is not good. made it back voltmeter showed 12.2 v at idle. alternator was putting out 11v // replaced alt. all good. moral is the gauge actually works! it does give a warning.
points for making it back without the wife noticing = priceless

 

Slow charge the battery to get it back up to a full state of charge, instead of driving it to have the new alternator do it. The alternator isn't designed to fully recharge a run down battery, its designed to quickly put back what we take out on a start, or other high drain short term load. Having an alternator attempt to recharge a deeply discharged battery can cause both to over heat & be damaged.

 

yes agree. fortunately in my case the battery was not drained all that much still showing over 12v on my voltmeter as i caught the bad alt. pretty quickly.
i will likely change out the battery soon as it's over 6 years old...

 

OK, 12.2 volts says that the battery was at about a 60% SOC, so it was down by about 40%!!!!

 

actually i was getting a little over 12v at idle and engine off. that told me the alt. was toast. bench testing the alt. could only manage 11v so i guess i was just reading the battery.
it seemed a normal figure for it with engine off. maybe it's time for a new battery ..
any recommendations? the current one is a 6+ year old die hard which has never given a problem.

 

If this battery has cell caps, remove them & check the electrolyte level & top up as necessary with distilled water, then put it on a slow charge, say 4-6 amps & see if it's SOC will recover & the new altenator will keep its charge topped off. A fully charged battery at room temp, at rest with no electrical load & the surface charge removed if its just coming off a re-charging, should read 12.6 volts or higher.

After recharging it, run this puppy by your favorite autoparts store for a no cost in vehicle electrical system checkup, via their portable electrical system tester. Have them do an under load test on the battery to see how its under load output does, then based on the test results make a decision on what to do about replacing the battery.

I typically get 8-10 years service from my OEM Motorcraft batteries.
Replaced the 99 Rangers OEM battery in 09 with another Motorcraft.
I have a Walmart Everstart MAXX in the 94 Taurus now thats going on 5 years & is doing ok.

In general, most batteries that have a no prorated three year replacement warranty will be a better made battery. So choose the least expensive you can find & go with it & keep it well maintained & it'll likely work real good & last a loooong time!!!!

Another clue, choose the heaviest of the above & you'll likely be getting one with the largest plate surface area & thats better.

Also choose the one with the highest Reserve Capacity (RC) rating, as its a clue to the plate surface area.

So, longest free replacement time, heaviest weight, highest RC & lowest price yields the best bang for the battery buck in most cases. My local Walmarts also offer the highest dollar for the old battery ($10), so figure that in along with the fact you can find a Walmart almost anywhere 24/7, in case you have warranty problems.

If your going to replace the battery based on lowest cost alone, post back & I'll put up a link to some serious discount codes to use at Advance Auto. You can use the promo codes to order on line & pick up in the store, (no shipping costs added) all of which can save a bundle. Did this last year when I finally had to replace my 15 year old marine cranking battery & saved 40% on the replacement battery cost!!!!

More thoughts for consideration, let us know how it goes.

 

thanks for the post pawpaw. not sure what i'll do in the end but the 1st chance i get when this cr#p weather gives up will be to check the levels in the existing battery. i even have distilled water on hand..
if you post up the advance auto codes am sure someone will be able to use them. i believe advance's batteries are also made by johnson controls ?