alternator or something else?

[cfan10]

Okay got a jump Tuesday because when I turned the key all I heard was click. Had my mom to go and start it Wednesday everything was OK. So, today I went over to take it out and no start didn't even give a click this time. It has two cheapo batteries connected now. I'm guessing because it has a cb radio installed/radar detector/too many speakers and those strip lights everywhere.
Had auto zone check the alternator when I bought it said it was OK, checked batteries too and the aux batt needed a charge, didn't do it. That was the beginning of last month.
Sometimes when I start it if the CD player or radar detector is on it will kill, turn it off and it starts right back up with no issues.
Does it sound like it needs an alternator? As always thanks in advance.

90 suburban 350tbi dual battery

[Bigstevex4]

Need to check volt meter running should be around 14 volts. but it sounds more like battery. if you can just jump it to start then it runs ok.

[cfan10]

Thanks...

[wilkin250r]

When your alternator goes bad, generally the car will run and everything will work just fine, but only for a while. Then everything will suddenly go dead, usually while driving. The engine just shuts off, no noise, and you coast to a stop and wonder what's going on.

That's because your car will run off your battery, until the battery dies. Often, because the car won't start, you get a jumpstart (which puts a small charge back on your battery) and off you go, happy as a clam. Few miles later, it dies again, that small charge you put on your battery just ran out.

The OLD SCHOOL method to test your alternator was to start your vehicle and disconnect the battery. If it stays running, then your alternator is good (because the alternator is providing electricity to keep it running). If it dies as soon as you disconnect the battery, it means your engine was using the battery for power, and the alternator isn't providing any. ***However, I would NOT try this if you have any computer-controlled elements in your car (Like TBI, for example), removing the battery from the system could damage the electronics**

THAT is a bad alternator, and it generally doesn't affect the operation of other electronics, and it's generally not an intermittent problem. It's all or nothing. If you have other electrical problems, like a CB radio that will kill the engine because of some electrical gliche, the problem is likely NOT in your alternator, it's somewhere else in your electrical system.

[cfan10]

^thank you kindly for the breakdown of the system. I'll replace the battery next week. Good day.

[C30Steve]

Before you go spending money on batteries and alternators try cleaning your battery cables. Disconnect the cables from the truck and use fine grit sand paper to clean all contact surfaces. Also clean and tighten the other end of the cables when they attach to the block and the starter.
Half the time, this is the only repair required.

When you are confident that you have a good connection at both ends of both battery cables then you can diagnose what the problem is.
To diagnose an alternators problem follow these steps;
attach a voltmeter to the battery, at rest with the engine off you should have close to 13 volts.
start the truck up, at idle with all accessories off you should have a reading on the meter that is higher than the base reading for the battery, approx 13.5 volts.
Still at idle turn on all accessories including high beams, wipers and a/c (if equipped), you should still have a reading all least equal to the base reading of battery. If the reading is lower than the base reading your alternator is weak or undersized for your accessories.
To check for an over voltage problem turn all accessories off and increase engine speed to about 1500 rpm. Your voltage should never go higher than around 14.5 volts.

To check the battery you need a voltmeter with a load tester built in.It is usually easier to see if the battery will hold a charge for a few days.

Hope this helps.