bmw z4 low battery, 15V alternator?

Q

qzmptg1

New member
BMW Z4, 5 years old, probably original battery.

Warning lights came up all over the dashboard. Owner (friend of mine) took it to a local mechanic who said the battery was flat. Shame they did not check it when the engine was running; see below.

Mechanic said it was fitted with a start stop battery. It is not a start stop car as there is no over-ride switch. (I am reading the manual now which is about as difficult as completing a Phd). It is an auto box.

I interrogated the car's gps / computer via nobs and buttons (the car is like nothing I have ever seen; very sophisticated) and it shows no saved errors or "check" points. The only warning is a flat battery when ignition is turned on.

I just found the battery at 11 Volts after owner had taken it for a drive. Engine started (goodness knows how) and I measured the alternator kicking out 15 Volts !

Engine off after 1 minute and back to 11 volts.

I have connected it to a 50W solar panel and solar controller so the battery should only get 14.5 volts max and then be controlled by solar controller. I don't have access to my Ctek charger.

It is fair to say that over the last year and lockdown the car was not used much.

So I am questioning whether alternator screwed, or battery screwed, or both, OR just battery screwed and alternator is compensating?

(1) Question. Is it a stop / start car (I am reading manual to find out)
(2) Do stop /start cars have alternators kicking out 15volts?
(3) Any other advice? Such as alternator could be ok, but battery is screwed. (Battery looks like maintenance free type; if my car I would prise off sealed plastic and check electrolyte levels - assuming not AGM or gel, but I can't do that here)

I know a mechanic who is excellent but has a long waiting list and the car will go to him for a battery change if he deems it so (I dare not on such a complicated machine), so any advice to keep things ticking would be appreciated. Actually, I can source the correct sized battery and Cold Crank capacity, so it I use another batter to keep terminal live as I swap batteries, is that feasible or not sensible; I have done it on my old cars where I did not want to bother inputing the radio code again.

Back to reading the 293 page user manual, now.

Thank you for any pointers.
 
if its a soft top e85 then just a regular battery required, if its a hard top e89 it does use a start stop despite not actually being a stop start car
 
I have placed battery on charge for now.

Is it acceptable to charge directly to battery or should I go via the contacts in engine bay?

Thanks
 
Better to put the charger direct to the battery in the boot,, if you use the points under the bonnet it will charge the battery but the length of cable from there to the boot will cause a reduction in the voltage reaching the battery. Opposite applies if you are jump starting the car, use the under bonnet connections, they are nearer the starter motor so no reduction caused by the boot to engine cable.
 
Thanks.
I naturally went into the boot, but another forum said to charge via the terminals in bonnet; did not give a reason.

Anyway, it has been on for a few hours in the boot now.

Tomorrow or next day and I will knwo if battery is good, acceptable or knackered.

Thanks
 
Don't hold out much hope on your battery recovering given what you have described, reckon you will need to replace it. Once replaced run the engine and put a volt meter on the batter terminals and see what the alternator is putting in to it, should be around 14.5volts.
Anything less would point to a failed regulator pack in the back of the alternator, anything widely above would also point to a bad regulator pack. If the bearings in an alternator are still good it can be cost effective to just replace the regulator pack which includes the brushes. Circa £30 compared to £100+ for a recon alternator.
 
colb said:
Don't hold out much hope on your battery recovering given what you have described, reckon you will need to replace it. Once replaced run the engine and put a volt meter on the batter terminals and see what the alternator is putting in to it, should be around 14.5volts.
Anything less would point to a failed regulator pack in the back of the alternator, anything widely above would also point to a bad regulator pack. If the bearings in an alternator are still good it can be cost effective to just replace the regulator pack which includes the brushes. Circa £30 compared to £100+ for a recon alternator.
Click to expand...

The e89 ibs gives odd charging voltages depending on wether the car is accelerating or braking & also the voltage of the battery, it’s classed as regenerative braking by bmw. (It can vary from 12v to just under 15v)
Because of this system it’s recommended to charge the battery via the under bonnet terminals to prevent the ibs system from being bypassed :thumbsup:
Rob
 
I’d get the battery changed ASAP as you risk causing the electronic parking brake failure, either order a replacement AGM battery and fit it yourself and get it registered later or book it in somewhere that will fit and register it for you, these cars a very sensitive to low battery voltage and can cause numerous faults.
 
You must log in or register to reply here.
Back
Top Bottom