Battery not keeping charge/charging (very strange)

[thenixtone]

Hi guys,

So before I take my lovely car to the auto electricians, I'd like to try and figure it out as I know they can be quite pricey.

 

Here's the story...

With a brand new battery, the car will last a month if I drive it every 3~ days or so. After the 3-4 weeks, the battery will be flat. This means  I have to jump start it after said time. (If I jump start the car and drive for 30mins, there is not enough charge for a 2nd or sometimes 3rd start)

Boot light does not stay on, the car used to have an alarm system which has since been removed by the previous owner (could be the issue). Radio is ancient and a bit f**ky (could also be the issue, clarion head unit).

 

With me trusty multimeter and voltmeter, the alternator is definitely charging the battery at a nice 13.99v whilst running, however when I flick the headlights on it drops voltage from 14~ to 10~ then back up again (makes the car stutter a tiny bit). 

 

Here's the f**ky part.

 

When the jumper leaders are attached to the good car, my skyline runs beautifully. When I remove the cables, or start it with a good battery, the car splutters a little bit and runs like ass, just idles very rough and up and downy (when driving its fine). Thus I believe this to be a bad earth somewhere, thus probably a parasitic drain etc?

 

From my research and limited electrical knowledge it seems I am SOL and the auto elec is the only option... What do you guys think, is this common?

Edited May 9, 2020 by thenixtone

[GTSBoy]

Well.....look for the parasitic drain. Start at the battery. Put the multimeter on a current setting in between a terminal and the loom. If you find (significant) current flowing, then proceed to do the same at each fuse.

But I'd be willing to bet that you're alternator is not working correctly, based on what you say about what happens when you connect it to a car that has a working alternator.

[trel]

If you know how to remove your alternator do It. I can be almost certain it's the voltage regulator, the armature rarely is a failure point. 9/10 It's the reg. Check earth points too never a bad idea while you're checking electrical. Not a massive job for an auto elec worth their salt.

Edited May 9, 2020 by trel

[thenixtone]

54 minutes ago, GTSBoy said:

Well.....look for the parasitic drain. Start at the battery. Put the multimeter on a current setting in between a terminal and the loom. If you find (significant) current flowing, then proceed to do the same at each fuse.

But I'd be willing to bet that you're alternator is not working correctly, based on what you say about what happens when you connect it to a car that has a working alternator.

Yeah see that's the weird thing, it's supplying enough voltage to the battery (14v), but I agree I think it is the alternator

 

And if only I had a charged battery so I could check the drain with the car off lol

Edited May 9, 2020 by thenixtone

[GTSBoy]

I thought you said you had a good car. There's your good battery. Just bring the power over with the jumper leads.

[thenixtone]

Auto elecs said the alarm system (that was meant to be disabled) was still drawing 0.2 amps with the car off. Lmao

 

New battery fixed the grounding issue with the rough idle. Lets hope their fix to the alarm wiring stops it from draining.