Diagnostic help please - alt / battery

[messar]

After sitting a few days, engine barely turns over, lights dim.

If left overnight, fires right up.

I figured this is dead battery, but when I checked the voltage at the battery when running, it's reading 13.0-13.2. (should be 14.2 I believe)

I did a load test on the battery, and it shows weak (but not bad).

Given the low voltage, I'm thinking more that it's an alternator issue - is there any way to be sure? (or both alternator and battery for that matter). Is it possible for a bad battery to pull down the voltage that much??

Failing that, where's the best bet to get a replacement.

Thanks,

Matt

 

[robot808]

Matt,
What year is your Disco?
Advanced Auto uses a Midtronics battery tester that can also check your alternator.

 

[SGaynor]

How old is your battery, and what make? If older than three years on a "regular" battery (5 for a top end one), I would recommend replacing it.

Low voltage can be due to a bad cell (6 cells X 2V). Given that it dies after sitting and the load test showed it was weak, that sounds more like the battery than the alternator.

 

[RoverbyProxy]

If you have a bad battery your alternator will never charge properly, my guess, replace the battery.

 

[antichrist]

The cheapest place to start is to make sure all your connections are clean and secure. Corroded or loose connections, including the grounds, will reduce your charging voltage and never let your battery get fully charged. I'd do that then check the charging voltage again, and go from there.

 

[messar]

Thanks for the comments.

It's a 2000 D2

Robot808 - would be interested in what you have for the tester (model and what you're looking to get) - I've sent you a PM

I went out last night, and pulled off the cables, and cleaned everything - seems to be a bit better (14v at the battery when running).

My thought from the very beginning was bad battery - it's the low reading when running that really threw me - I'm still a bit confused actually.... I would have guessed that with a poor battery connection, the alternator wouldn't see as much load from the battery, and put out full voltage.

I don't know how old the battery is, and will replace it just in case, then go from there (fingers crossed).

 

[robot808]

Sorry messar, bad grammar on my part. Edited my post to make clear I have a spare alternator.