Jeep battery or alternator dead?

[GilpinGuy]

I'm pretty good under the hood, but this has me stumped. Intermittently, when I start the 99 Wrangler (4.0) it acts like the battery is almost dead. I hook up the handy dandy battery tester (engine off) and it shows full charge. I start the engine and the tester says alternator is charging at 100%.

I put in a Napa remanufactured alternator last summer and the battery is 2 years old. WTF is going on here? What's wierd is that it's intermittent.

ETA: I already cleaned the battery terminals and the connections to the alternator look clean.

[68Charger]

I don't know what tester you're using, but do you have access to a digital multimeter?
I prefer real voltage readings over an good/no good light

It could also be a dead/shorted cell in the battery- would show those symptoms... have the battery load tested... unlikely at 2years, but you never know.

[Irving]

Check grounds?

Wait, when you say act like the battery is almost dead, do you mean a slow turn over? Could it be the starter is getting tired?

[GilpinGuy]

Check grounds?

Wait, when you say act like the battery is almost dead, do you mean a slow turn over? Could it be the starter is getting tired?

This is possible I guess. 193k on the odometer on the original starter. I never had a starter go bad like this before though.

[Graves]

How many amps is the starter pulling?

[GilpinGuy]

How many amps is the starter pulling?

No clue. I'm pretty ignant on electrical stuff to be honest.

[GilpinGuy]

I think I have a multimeter around here somewhere. I'm not real good with electrical stuff so I've used it very rarely. I forgot to mention that I did the battery down to nothing a few weeks ago - left a compressor plugged in to the cig lighter and the ingnition on all night.

[DenverGP]

I've seen similar problems from a corroded battery cable, connector, or battery terminal.

Pull both cables off, give them a very good cleaning, rough up the battery terminals, and re-tighten.

I had one battery cable, looked ok, but a twist of the connector at the end of the cable and the wire just disintegrated, it was completely corroded inside. Turns out the battery terminal had been cracked, and was leaking a tiny bit of battery acid right at the terminal for a while.

[Graves]

Should be able to get a full ESC (electrical test) for a small(ish) or perhaps free at a local shop. What kind of tester are you using to check the battery? Deep cycling the battery is no bueno.

[SideShow Bob]

Here's a quick couple of tests to check the alenator, while running, see if a wrech will stick to the back of the altenator. If not weak altenator. Then Start the jeep, pull the positive battery cable, then start turning on the electrical items..... Headlights, radio etc.... Until everything is on or the jeep dies. If the jeep dies, bad alternator.