P38A Battery - Bubbling and leaking

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Montyjohn

Montyjohn

Well-Known Member
Posts
251
Location
UK
I've been having some battery problems recently.
Didn't move it for a couple of weeks and it had 2.6V. Hmmmm.
It's taken a charge and starts fine now.
Not sure if there's an electrical drain, or a duff battery yet.

I get loads of corrosion on the terminals, and the top of the battery is always wet.
Voltage when running is 14.6V.

It has no visible vents on the battery. So no rubber bungs to remove or anything like that.
With the caps off and charging, I can see it bubbling inside. Assume this is normal. Water levels also look normal.

Before I just swap the battery, I want to make sure the car isn't killing it.
Do these symptoms mean anything to anyone.

A question I do have is how is the water getting on top of the battery? There are no cracks, but after a charge it's always there.

PXL_20250127_103815322.jpg


PXL_20250127_103849031.jpg
 
yes a battery will bubble softly while charging. if its violent then its dead, or the charger is over charging.
how much airgap is there between the acid and the opening? should usually be at least 1/2 inch, ie 1/4inch max acid covering the cells.
once its fully charged, connect it to the car and crank the engine while measuring the voltage at the battery, depending on battery size it should be around 11v while cranking and before it starts
 
kermit_rr said:
yes a battery will bubble softly while charging. if its violent then its dead, or the charger is over charging.
how much airgap is there between the acid and the opening? should usually be at least 1/2 inch, ie 1/4inch max acid covering the cells.
once its fully charged, connect it to the car and crank the engine while measuring the voltage at the battery, depending on battery size it should be around 11v while cranking and before it starts
Click to expand...
I'd roughly 2" between the opening and the top of the acid.
But I can't see the cells so assumed it's normal.

SO I've done some investigating and learnt two things.

1. There are little vents on the capcs. I found it bubbling though one of them. Removed the cap and it was gently bubbling 2" down. Why or how it's jumping to the vent in the cap I have no idea.

2. I have a parasitic drain. When I first start measuring I get 2amps. After the air suspension calms down, it drops to about 1 amp to 1.5 amps. Then after 30 seconds it drops and stays at 0.7 amps. I assume forever.

So I guess I need to investigate this RF receiver thingy. Any other obvious candidates to to inspect?

Once I've fixed the leak, I'll swap the battery and see how I get on.
 
Grrrrrr said:
RF receiver favourite, especially if you have a wireless weather station.

Or after-market stereo.
Click to expand...
It has a standard radio.

I've just unplugged the RF receiver. Blue wire and power, same result.
At least I now I know I have the MK2 receiver. It's a crappy thing, key only works right by the rear window.
I sort of wanted this to be the issue to justify replacing it, but looks like I need to look elsewhere.

Is it now just a case of pulling one fuse at a time? Because I really don't want to.
 
Montyjohn said:
It has a standard radio.

I've just unplugged the RF receiver. Blue wire and power, same result.
At least I now I know I have the MK2 receiver. It's a crappy thing, key only works right by the rear window.
I sort of wanted this to be the issue to justify replacing it, but looks like I need to look elsewhere.

Is it now just a case of pulling one fuse at a time? Because I really don't want to.
Click to expand...

That'd be a good starting point.

If it has headlight wipers then check they are "parked".
 
Montyjohn said:
It has a standard radio.

I've just unplugged the RF receiver. Blue wire and power, same result.
At least I now I know I have the MK2 receiver. It's a crappy thing, key only works right by the rear window.
I sort of wanted this to be the issue to justify replacing it, but looks like I need to look elsewhere.

Is it now just a case of pulling one fuse at a time? Because I really don't want to.
Click to expand...
Pull the power connector from the RF receiver, the receivers can develop an internal fault causing battery drain. Disconnecting the aerial as you have done will make no difference in that case.
14.6 volts when running is good for a normal automotive lead calcium battery, but your battery looks like is not a lead calcium battery in which case the voltage is too high and will account for the excessive bubbling. As it has been down to 2.6 volts, it's probably knackered.
 
Go through the battery drain checks in the BECM System Info doc. I'm sure I posted it on here a while back, but here's the section again just in case.
 

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pwood999 said:
Go through the battery drain checks in the BECM System Info doc. I'm sure I posted it on here a while back, but here's the section again just in case.
Click to expand...
So stepping towards the answer. Thanks for the document.

Mine does drop from 1.5A to 0.7A (approx 800ma reduction) but after about 20 or 30 seconds. Not two minutes as the document suggests.
Just to confirm, I pulled MF1, 4 and 5, and the current started at 0.3A, then after maybe 30 seconds dropped to 0.09A. So it's clearly the BECM staying awake.

I know it's not the RF Reciever, as that isn't even in the car at the moment.

SO I guess I need to go through table 1 for things that could be activating the BEMC.

Hang on, item no. 1 is the bonnet open sensor. Do I need to bonnet closed for the BEMC to go to sleep?
 
Montyjohn said:
So stepping towards the answer. Thanks for the document.

Mine does drop from 1.5A to 0.7A (approx 800ma reduction) but after about 20 or 30 seconds. Not two minutes as the document suggests.
Just to confirm, I pulled MF1, 4 and 5, and the current started at 0.3A, then after maybe 30 seconds dropped to 0.09A. So it's clearly the BECM staying awake.

I know it's not the RF Reciever, as that isn't even in the car at the moment.

SO I guess I need to go through table 1 for things that could be activating the BEMC.

Hang on, item no. 1 is the bonnet open sensor. Do I need to bonnet closed for the BEMC to go to sleep?
Click to expand...
I believe you do
 
Montyjohn said:
So stepping towards the answer. Thanks for the document.

Mine does drop from 1.5A to 0.7A (approx 800ma reduction) but after about 20 or 30 seconds. Not two minutes as the document suggests.
Just to confirm, I pulled MF1, 4 and 5, and the current started at 0.3A, then after maybe 30 seconds dropped to 0.09A. So it's clearly the BECM staying awake.

I know it's not the RF Reciever, as that isn't even in the car at the moment.

SO I guess I need to go through table 1 for things that could be activating the BEMC.

Hang on, item no. 1 is the bonnet open sensor. Do I need to bonnet closed for the BEMC to go to sleep?
Click to expand...

Yes. I drop jump leads down under the car when testing.
 
I have a spare battery with a pin hole near one of the terminals. When left outside its OK, but if charged, this terminal acquires a fur coat of powdery oxide. Leaking battery acid is always the cause. Acid should cover the internal plates but not drown them because it will escape when charged and corrode the battery shelf, paint etc. Before 'ealth n safety' gripped our planet, a common test was to short the battery terminals with a beefy file or similar because iron is less conductive than copper and short circuit current was more controlled. A proper garage would use box stacked with a series of 1" carbon plates, squeezed by the lead screw from a small lathe. It applied a short circuit to the battery but, with more control and the posh version was fitted with an iron core ammeter to read battery current. For this s/c test you're looking for gentile and consistent bubbling from all six cells. If one or more cells boil, they're the cells that are duff and cause the battery to self discharge. I have successfully used BatAid pills for a tired battery but, they don't fix a faulty cell. Perform this test outside because of gassing and expect a few sparks at the terminals but, it will give you a 'Go - No Go' answer from each cell as it gasses. This is not battery advice, but a historical account of my experience with suspect batteries. :)
 
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