battery problem

I have a 99 Suburban that has been having a battery problem. If I leave the battery connected it sometimes discharges enough to need to be jumped. I normally use the quick disconnect I put on it every time I shut it down for
any length of time. It was so bad yesterday that I needed to jump it 3 times. I took it to Walmart and the battery was bad, the 3rd one in 2 years. Is it possible that the problem is all in the battery?
Related question, I would like to set up a dual battery system. Instead of a battery isolator, could I just put in 2 power diodes in the charging cables?
Mike D.
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On Thu, 30 Jul 2009 18:01:49 -0500, Michael Dobony

I had a similar problem earlier this summer when the battery in my '01 Blazer wouldn't maintain a charge. My mechanic found that the starter had a short that was drawing a charge and draining the battery.
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wrote:

I've had that happen on more than one car in the past. Sometimes the investigation takes a while and the time spent adds up to a labor charge. Often: dome lights are the offending part.
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Hi Mike No expert here...I think I would get a small 12V bulb and jumper wires to it and remove a battery cable and put in series....if bulb lites you know current is flowing from the battery. If so, then start putting bulb in series with other circuits to find the leak to ground. I think the alternator can leak if it's going bad, but not sure...you can check with the bulb hookup. Good luck Pete
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How long do you let it sit disconnected? Its 10% per month or so discharge in this state. Below %50 charge you will get sulfation. A battery maintainer would be a good investment under these conditions.
Otherwise, there is a short, or a bad load in the system. Or even just a dirty battery.
I gather by 1999 they figured out that the lead washers on the side terminal posts compressed to the point the screw caused a leak in the terminal. Might want to see if there are there and replace them if they are.
Good luck
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Very possible on a bad battery. I've had to replace 2 AZ batteries in 3 yrs. due to internal bad connections in the battery. My fault for buying cheap A Zone batteries but when I needed one they were open and convenient. Use a isolator if your going to be starting with the 2nd battery., the power draw on cranking will blow diodes, that's why most isolators are relay based. Not too many diodes will withstand several hundred amps of draw.
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On Mon, 3 Aug 2009 09:38:24 -0400, Repairman wrote:

????? The diodes in an isolator go between the alternator and the batteries, not the battery and the starter. It never sees "several hundred amps of draw." A 100 amp alternator will only feed a total of 100 amps.
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On Fri, 31 Jul 2009 08:09:49 -0700, Bill wrote:

?????? The second FACTORY battery is for diesels, not gas motors. Relays cause a good battery to drain into a bad battery. Totally a stupid idea. Battery isolators keep this from happening by individually charging the batteries and prevent the good one from draining into the bad one.

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On Fri, 31 Jul 2009 19:14:28 -0400, Stormin Mormon wrote:

been there, done that. Nothing seems to be drawing the power when I test. It is an intermittent thing. Most days it is fine, then every once in a while, about 1-2 times a week . . .
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Do you have a light under the hood that comes on when the hood is lifted up (gravity switch)?
I had intermittent problems with a '96 Tahoe that had one. The switch was not sliding correctly, and would leave the hood light on (even if I hadn't opened the hood. The switch would move to the "on" position, and stay there). The only way I noticed it, is one night, I could see a faint glow coming from under my hood.
I just disconnect the connector at the under-hood switch, and problem solved.
John
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On Mon, 10 Aug 2009 19:13:55 -0500, John wrote:

I do rounds every night and would have noticed that. More likely is the glove box light. However, I have noticed something unusual. Normally the volt meter shows at least 13.5 v, sometimes up to 14.5v. However, once in a while I am lucky to get 12 v. If I turn the front vent fan off the v jumps back up to 13.5 or 14.
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On Tue, 11 Aug 2009 10:38:43 -0500, Michael Dobony

Sounds like the alternator has very low output.
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On Tue, 11 Aug 2009 22:02:02 -0700, Ashton Crusher wrote:

Today it did. If I take it out it does fine on the machine. Today it did about 12.5 volts at idle and peaked at 13.6 at 2000 rpm. First thing is to change the alternator wire tomorrow to check it. However, today it was totally dead when I went out there to start it up. I let it idle for a while and then drove about a block and it died completely and would not start. My wife brought the car and jumped it. I then drove it for quite a while and it would not start again. I took it to Auto Zone and got the above results. It just starts now and the back window barely closes. Also note that the previous post numbers are from the dash volt meter, not a real volt meter. However, the AZ numbers support the dash numbers pretty close.
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Mike you should check the current draw form the battery when car is stopped.Just disconnect neg terminal and put a current meter in series with it.Current should be low, this is a guess but 100 ma or less. If it is under 100 ma look for charging problems, some suburbans have cheap alternators in them they may check good but don't charge all the time. mainly when they get hot (The diodes). What does your dash volt meter read? should just be under 14V after running for a while. Watch it closely it should always be near 14 when car is moving engine over 1500rpm. if it is lower than you may have an charging issue. This can kill batteries. Alternators are funny they will charge for a while untll diodes get hot then they drop off to lower output.(Due to leakage) you can see that with the voltmeter.
Yes you could used diodes if you know how to design the circuit properly. They may require heat sinks and properly sized wires. The forward (on) voltage drop across the diode is a problem during hard charging you need to find diodes with very low forward voltage drop vs the current. This will reduce the power dissipation and thus the heat sink size.
Good luck. Joe
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