HELP battery not holding charge

[issac]

Allright I have a "87 silverado V10 with a 355 sbc the truck has a new Duralsast gold battery and the alternator was tested twice at autozone and passed both times. The truck runs great if I jump start it but the starter just clicks or turns the motor over once or twice if I dont jump it. But goin down the road last night I went an turn on the haed lights and the motor started to cut out real bad and the volt guage hit 8v(the lowest it goes) well the truck ended up dying so I had a friend jump start it and got down the road a little ways and turned the lights on and it started cutting out again so thats when I realized that was the problem so I turned them off and it went great well I found out it did the same thing when the blinkers came on and when I tried to use the power windows the volt guage would bottom out and the windows moved real slow and of course this all happend in the middle of the one and only storm in 3 months or so. So can anyone help me or give me information about the problem please.

[issac]

Allright I have a "87 silverado V10 with a 355 sbc the truck has a new Duralsast gold battery and the alternator was tested twice at autozone and passed both times. The truck runs great if I jump start it but the starter just clicks or turns the motor over once or twice if I dont jump it. But goin down the road last night I went an turn on the haed lights and the motor started to cut out real bad and the volt guage hit 8v(the lowest it goes) well the truck ended up dying so I had a friend jump start it and got down the road a little ways and turned the lights on and it started cutting out again so thats when I realized that was the problem so I turned them off and it went great well I found out it did the same thing when the blinkers came on and when I tried to use the power windows the volt guage would bottom out and the windows moved real slow and of course this all happend in the middle of the one and only storm in 3 months or so. So can anyone help me or give me information about the problem please.

[timthescarrd]

Had a very similar problem, it was a bad alternator, AutoZone tested it three times right in front of me and it passed each time but it was still bad, swapped it and no more problems.

[bd]

I see this is your first post, so welcome to the site from Central California!

1)  Check the positive battery cable for clean, tight connections to the battery and starter.

2)  Check the fusible links at the starter and firewall junction block (if they stretch like a rubber band, they're bad).

3)  Check the battery to engine ground connections for corrosion and tightness and service them as needed.

4)  Check the alternator mounting to the engine (the alternator grounds to battery through its mount).

5)  Inspect the wire and terminal end connections to the alternator, starter and battery for corrosion, tightness and/or discoloration caused by excess heat (poor connections can cause wires to melt and burn, degrading electrical connections even further).

If you have a single-wire alternator conversion, ignore the following two steps:

6a)  If you have a 12-volt test light (not a voltmeter), with the key OFF/engine OFF, clip the test light to ground and probe the two alternator harness connections to the integral regulator (#1 should be dead, #2 should be battery voltage).

6b)  With the key ON/engine OFF, re-probe the regulator connections (#1 should be dim, #2 should be battery voltage).

[Irish_Alley]

it might be its able to charge at a lower demand, but when its a higher demand it just cant keep up