My 86 doesnt get driven very much so naturally the battery dies after about a month of sitting in the garage. Is it normal for the battery to be no good after all this time? The battery is about 4-5 months old.
I have jumped the car which took about 15-20 minutes of charging and I let it run for another 15 minutes.
After letting it run I shut her down and tried restarting her. The battery was back down to about 10.5 volts. Is this normal or could I possible have more going on here? This the third battery I have replaced because of this (free return at wallmart).

 

Definitely something wrong here. It sounds like you have some sort of current drain that is killing the battery. The early C4's don't have much in the way of electronics (lik C5's for example) that would be using up the battery. My 87 with an Interstate can sit for a good 3 months before the battery drains to where the starter runs slow but it will still start.

You didn't say what you used to jump/charge the battery but a discharged battery should take a good 30-45 minutes at 20-30 amps to fully charge up. The alternator is not for charging a battery as it's not designed to produce large amounts of amperage for long periods of time. That will kill an alternator over time.

A battery that is fully charged and in good condition will show about 12.8v across the posts. When discharged, it would be at 12.1 or so. If you saw the 10.5v on the voltmeter display with the ignition switch in the ON position, that's about right for a discharged battery with the drain from the key on position.

Of course it's also possible that your alternator is bad. I would find a reputable shop and have them do a load test on the battery and have the charging system checked. This is done with the engine running and using equipment that places a heavy load on the electrical system.

If the charging system checks out OK, you can test for a current drain by placing a voltmeter in line with the negative battery cable. Remove the battery cable and attach the positive lead from the voltmeter to the cable and the negative lead to the battery negative terminal. Go to the fuse box and pull one fuse at a time to see if the reading drops. Pull one fuse, then replace it and go on to the next one. Once you see a substantial drop in the reading, your drain is in that circuit.

 

If it's going to sit for a month at a time, a Battery Tender (or equivalent) is a must-have. There are still things in these cars that are always-on (clocks, keyless entry, etc).

You also might consider disconnecting the battery if it's going to sit for a long time. Pick up one of those insulated ratcheting battery terminal wrenches and it only takes a couple of seconds to pull the negative terminal.

 

Not sure if this is normal but my 94 does this too, I usually get a bit more than a month though. I bought some quick disconnects for the battery. Installs onto the battery and negative cable and you can turm off power with a thumb screw. then you need no tools and it takes 2 seconds to turn off or on. Most vette places and auto stores should carry them.

-Dave

 

Im going to try your test.

I tried using a battery charger/tender from harbor frieght. I left it on for 24 hrs and it did nothing. Im starting the think the cheapo charger just isn't working because the battery level light on it is not coming on. So I jumped it with my truck.

You might be right about the alternator being damaged because I had cracked the housing in the past (missing alternator bracket) but replaced the cracked half. This might have damaged something internal.

 

Be careful trying to run the car on a close to dead battery, as it can damage the alternator.

 

Lead acid batteries self discharge up to 1% each day even disconnected. During discharge lead sulphate collects on the plates. When you charge the battery, the lead sulphate converts back to lead and sulfuric acid. If you let the battery sit 4+ wks, the lead sulphate becomes hard and upon charging, it will not convert back to lead/sulfuric acid and lead sulphate is an insulator which greatly reduces the amp hour capacity of your battery. You wind up with effectively a motorcycle battery or no battery at all and it will not draw current if you try to charge it. At that point you have a door stop.
Lead acid batteries take a long time to charge up and draw large current at first and this heats alternators and shortens their life. Alternators are not made to charge up dead batteries. Also, 15 minutes of running an engine will put very little charge in them. You need to charge a discharged car battery overnight with a battery charger. If you don't use the car much, then buy a battery tender and use it. Battery tenders (commercial name) measure the battery voltage and when they lose 10% of charge, they charge the battery up and turn off. If you use a battery tender, you will experience normal battery life. Letting a battery sit for a month is certain death!
To measure leakage current, remove the neg battery cable and connect an ammeter (not a voltmeter) between the battery neg post and the cable. After the courtesy lights time out you can switch your VOM (voltmeter, ohmeter, ammeter test instrument) to lower full scale current to read the leakage current. GM says leakage current should not exceed 50 milliamps. My 87 draws 27 ma and causes no trouble.
You can tell the state of charge in your battery by measuring the battery voltage at its posts. 12.0 volts and below, discharged, charge your battery up overnight with a battery charger. 12.9 volts and above, fully charged and linear in between.
Hope this helps.

 

I bought a new battery charger (quick charge/jumpstart/trickle charger) from sears. The battery is full and charged and I haven't noticed any significant current drain. Im still going to test it with my multimeter as suggested just to be sure I have no problems. Thanks for the help guys.

 

I notice the earlier c4's have more complaints about this. for one thing I think the radio (believe it or not) uses battery to keep time and settings, and sometimes, hood lights, don't work right.

 

 

My mom has a 60 series group 75 AC Delco battery in her Trans Am. She only drives it one every week or two. Sometimes it sits for three weeks. And its been holding up for a couple of years now. So, if you replace your battery. You might want to give it a try. It is $75 at the dealer. Though you could get a professional AC Delco battery, but they are around and over $100.

Autozones batterys have a little better warranty, but they are open and can leak. My 5 year old Autozone battery in my Firebird has left corrosion all around the battery. It probably leaked from the top. The AC Delco batterys are sealed. So, less chance of leaking. Plus, I really like the handle on them too. It is a nice looking battery.

 

You are killing the batteries. Every time you let the battery go dead, it takes months off of it's life. Jump starting a dead batt is hard on the batt, alternator , and electronics.

Keep it on a BATTERY TENDER.

 

To give you an idea what a well maintained battery can do; My starting battery on my duck/fishing boat, a Delco Voyager, was purchased in 1997 and has been used continuously since then. I don't use a maintenance charger but only the motor is connected. It still starts the boat like it is new. I have worn out two outboards on this battery and am on my third.

Something in your electrical system is draining your battery. Get a quick disconnect unit and use it between starts.