Sudden Battery Drain: Causes & Fixes

Hello,

I'm new here, and until now, I've only read this forum as a guest. Therefore, I must first express my sincere admiration. There's such profound expertise here that, as an amateur tinkerer, I can only tip my hat and bow in awe.

'I've been having a problem since last week that isn't necessarily specific to diesel vehicles, but I'm asking anyway: Last week, I installed a hands-free device, and since then, I've experienced an issue that makes it seem like my battery is defective. The car starts poorly or not at all after being parked for just a few hours, and the instrument panel lights almost go out completely, meaning the on-board voltage drops completely. I've already removed the fuse for the mobile phone, so the battery shouldn't be discharging through that.'

However, what makes me suspicious is the timing of the battery failure. Although the battery is older, I was still able to use the auxiliary heater to preheat the car for an hour in the spring, and the engine started well afterwards. Also, the car always started without any problems until the phone was installed, so the battery capacity couldn't have been that bad yet.

For the phone installation, I disconnected the negative terminal of the battery, but it is securely reattached. I even sanded the terminal clean just now. Could the battery be damaged when disconnecting the terminal?

The charging voltage is 14.3V. Without the motor running, the battery voltage is 12.8-12.9V. Unfortunately, I can't measure the discharge current at the moment, but I don't know why it should suddenly increase so drastically.

Does anyone have any ideas?

Well, death can come quickly, as it did for me. Your idle voltage seems a bit low; it should be 13 volts or higher.

Go to Bosch or VW with your fully charged battery and have them measure its capacity (cold temperature test). Then you'll see how much energy your battery can still store.
Check the battery acid level and, if necessary, top it up with distilled water.

The phone system shouldn't draw much power, even if a phone is connected to it. It's probably not related to that.

Hello.

Sudden battery failures like that can happen, but if it were me, I'd suspect something else.
Rest voltage 12.8-12.9V (I hope measured not immediately after turning off the engine, but rather 10-15 minutes later) is already quite good.
Charging voltage 14.3V, also OK.
You're saying you can't check the discharge current (standby current)?
"But you measured the voltage (down to the decimal place), right? Just connect a 1 ohm, 5W resistor between the negative terminal and the ground cable, and then you can measure it."
PLEASE DO NOT START THE CAR LIKE THIS!
Or just disconnect the power cable for a few hours and then reconnect it.
Do you know if it's just the battery, or is there a higher "idle current" consumption?
It's very simple and effective.


Regards,
Voss.
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Hi,
This is normal for lead-acid batteries. These batteries form lead sludge. That's why there's about 1.5 cm of space between the plates in the battery and the bottom. When the lead sludge reaches the plates, it causes a short circuit. In this case, one cell will be discharged, while the rest of the battery remains full. This discharged cell, which is already empty and has high resistance, will continue to discharge.

Over the years, the performance gradually deteriorates, and then the failure happens suddenly. (But you can't expect the battery to send you an email beforehand...)

Das wars dann. Buy new.

Andere Möglichkeit : du hast nen Kriechstrom drauf. Test:

Charge the battery, disconnect it from the vehicle, and leave it overnight. If it starts normally the next day (after reconnecting it), then look for parasitic currents. In this case, good luck.

Just connect a 1 ohm, 5W resistor between the negative terminal and the ground cable, and then you can measure it .
Ouch, it almost hurts that I didn't think of that.

The quiescent current was 25mA. Then I changed the battery, and lo and behold: it works again, and it can also be turned off for a whole night.

I had never heard of lead sludge before, but it sounds logical and also fits very well with my sudden battery failure (but an email beforehand would have been really nice ).

It's fascinating that the error occurred just as I was installing my phone.

Thank you for your support!