Can bad alternator damage the battery

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I had the alternator on my 2000 Explorer go bad the other day while on vacation. I was able to drive on battery power to a parts store 5 mins before they closed. (Just made in as the battery ran to low to start the truck.) Bought an alternator, and the tools needed and changed it in the store parking lot in the dark, an hour later I was back on the road.

Days later I drove 4 hours home, and checked the battery voltage the next morning and only got 12.4V Battery is about 2.5 years old, but has had a rough life so far.

Could the failing alternator have done damage to the battery?
 
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12.4V is low, but not incredibly low, 12.6+ would be ideal, as you probably know.

Deep discharges are very hard on starting batteries. It sounds like you didn't quite do a full deep discharge, but may have damaged the battery slightly. If you've left a door open or dome light on and deep discharged it often, it could be time for a replacement. You might be best off getting it load tested at a store. If it's still starting without issue, I probably wouldn't worry about it.
 
I would clean and check the connections, but a battery that tests between 12.4 and 12.7 volts is totally okay. To answer your question - yes. A bad alternator can eventually kill a good battery. But that is probably not your situation right now.
 
The battery has a free 3 year replacement warranty. I bought it from a friend so the paper work is not in my name not sure how they would view that??. He left it in a discharged state for 4-5 months (3 volts) before I got it. it has performed well for me over the past cold winter, but I have been reading about bad alternator diodes doing damage to a good battery
 
You might try discharging and recharging the battery a few times, to see if it rebounds. Leave some lights on, and check periodically until the battery drops to 11 volts. Then recharge. Do this several times, until the time needed for the voltage to drop to 11 stops getting longer (Stabilizes). I have had good luck doing this with AGM batteries, (Doubling the discharge time) but it very well could do some good for a conventional battery, as well. Just don't deep discharge it (Below 11 volts).
 
Is your friend still in the area? Maybe get it tested and if it fails, try get them to replace it. If they need the person on the paperwork, drag your friend out.

I think though, that if they tested it, it would pass, so you might not be able to get anything under warranty.

Cleaning the connections is a great suggestion. And, if you have a small battery tender, maybe leave that hooked up for a few days.

Being left at 3V for several months is very hard on a lead acid battery. I would just keep running it and plan to replace it at the first sign of slow starts.

It might be a good candidate for trying out a desulphator.
 
I had an alternator on a car once that charged and ran at 16 volts. Sure, the headlights were BRIGHT, but it did a number on the battery.
 
Originally Posted By: Bluestream


Could the failing alternator have done damage to the battery?


Absolutely. The alt & batt work together as a system & balance is crucial. When either one fails, it puts stress on the other component.
 
All you can do is watch it and see how the battery responds to the new alternator.

A bad battery will overwork and alternator and a bad alternator will ruin a battery as it discharges while you drive.

I've found modern batteries only have a handful of full discharges in them before they fail.
 
12.4 is unfortunately normal for a daily driven vehicle. The alternator is not able to keep the battery at a fully charge state due to loading and age. I have the same issues with both of my vehicles so i regularly pull the battery and put it on an automatic 2 amp charge until its 100%.
 
Do not! I repeat again: DO NOT perform deep discharge/recharge cycles on automotive lead-acid batteries. It will shorten it's service life.

lead-acid batteries are designed for quick/short bursts of high current (for starters) and shallow discharges only, and must be re-charged immediately or the sulphation will settle in and kills the plate.

Q.
 
12.4V at the battery first thing in the morning is fine to pretty good. I'd say that you don't have a problem here. If you have not checked the water level in a while then do so. Otherwise I think you are fine.
 
Originally Posted By: Quest
Do not! I repeat again: DO NOT perform deep discharge/recharge cycles on automotive lead-acid batteries. It will shorten it's service life.

lead-acid batteries are designed for quick/short bursts of high current (for starters) and shallow discharges only, and must be re-charged immediately or the sulphation will settle in and kills the plate.

Q.


+1 - Thats what Optima Yellow tops are for
 
Also keep in mind 12.42v is considered approximately 80% state of charge for flooded lead acid 12 volts which isn't that bad. Like I said top if off with a charger every once in awhile. Using less accessories can help keep it higher. Winteriis rough on all my vehicles, with heater, headlights, rear defroster and radio running regularly I get below 12.4v resting frequently. At a certain draw your actually discharging the battery while driving it. Compound that with short trips and it's no wonder batteries only last so long.
 
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