[Skyhigh]

I bought myself a "smart" battery charger today and decided to test it on the F36 which has not been driven for about 5 weeks now. Surprisingly, the charger determined the condition of the battery to be around 20-30% charge

The car is parked in a garage, the temperature has been around 20 deg. C.
The car (hence the battery) is less than 2 years old.

Is this a normal discharge rate? Last winter after about 6 weeks of inactivity, I started the engine without any problems once and then got a low battery warning. That I find understandable however given temperatures around 0 to +5 deg. C in the winter period. But in the summer?

What is your experience?

[Billfitz]

That's not impossible, though unusual in the summer. I do put mine on a maintainer when temperatures go below freezing, partly because I seldom drive more than one day a week in winter.

[Solidjake]

Which charger did you use? The one I have is CTEK

[Skyhigh]

DEFA SmartCharge

Are those generally suitable for use as maintainers?
It is supposed to smartly charge, then stop and go on idle for 1 week and then analyse and recharge again.

I am confused nowadays with all types of batteries - is it better to just let it discharge (to some extend) for prolong periods of inactivity and charge before use or to maintain it more or less fully charged? Not sure what's safer for the electronics either.

[Billfitz]

Don't let it discharge, it's not a NiCad. Storage batteries last longest when they discharge the least. A maintainer not only keeps the battery charged, it also supplies current to those devices in the car that never really turn off. Having the maintainer power those items also extends battery life.

[Skyhigh]

So is the CTEK / DEFA way of operation suitable as a „maintainer" for our batteries? The DEFA does not trickle charge, but as far as I remember that is not recommended anymore either...

I just went to see the charging process. In exactly 5 hours it has gone from 1 bar (out of 5) to 4. That tells me the reading can't be right!? It is a 4A charger, so in 5h it has charged 20Ah, best case. As it seems it will in total do about 30Ah. The battery is 95Ah if not mistaken....

[Skyhigh]

Ok, further results - apparently the status indicator is not reliable for our cars at least. This morning the 5th bar was still blinking (charging the last percentages). That has been like that for over 12h. Could be normal as the voltage/current drops at the end.

However: As soon as I opened the door of the car (and various modules were triggered), the charger indicator fell down to 1 bar. I closed all doors, switched off and on the charger, it analysed the battery and showed 4 full bars. A minute later it again dropped down to 1 bar on its own. 3 minutes later it turned 2 bars, soon after that 3 bars and then 4 bars ....

I'm thinking the F3x is having a number of consumers even when passive which mess up the voltage of the battery when measured. Main question remains whether the chargers can then ensure no overcharging and proper charging cycle!?

[Mr Podman]

Originally Posted by Skyhigh

I just went to see the charging process. In exactly 5 hours it has gone from 1 bar (out of 5) to 4.

You might have more success with an 8A or 10A charger rather than the 4A you are using.


podman

[Skyhigh]

Can't see how "success" can be dependent on the power rating of the charger. It only affects charging time.
My point above was that the mentioned speed is too high, which makes the indicated battery level unrealistic.

[Mr Podman]

You also may have a faulty charger.
In the last 10 years I bought about 7-8 battery chargers for different items (cars, boats, snowblowers etc.)

About half of those chargers didn't work properly.


podman

[Billfitz]

It's possible that your charger shows it to be charging, which means it's providing current, even when the battery is fully charged, with the current it's providing being that which the car uses even when not being driven. I have one of these to check the actual status of the battery:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

My maintainer is 2A, and never fails to fully charge my battery overnight in the dead of winter. You're correct that there's no need for more capacity than what you have, higher capacity is only of value if the battery has been allowed to go to a very low state of charge, if not fully discharged. With judicious use of a maintainer that will never happen.

[Skyhigh]

It did fully charge the battery eventually (after hanging on it for nearly 48h and the interruptions mentioned above when opening a door, etc.).
The last 1 bar of the scale took forever (almost a day) (partially explainable due to the reduced voltage and current in the last phase)

[Skyhigh]

Another related question - as it is implied, the BMW has some internal protection of the electronics during charging?

Since BMW strongly recommends use of the front connection points for charging and not connecting a charger directly to the battery itself.

[Billfitz]

I doubt it. The under hood posts are easy to access, the battery posts almost impossible. The one time I had to disconnect the negative terminal I had to use tools to remove a bracket to even get at the battery.

[natesi]

Arent you worried about developing flat spots on the tires -- if the car is sitting for 6+ weeks? Why not just take it for a 30 min drive once a week and not worry about any of this?

[Skyhigh]

Originally Posted by natesi

Arent you worried about developing flat spots on the tires -- if the car is sitting for 6+ weeks? Why not just take it for a 30 min drive once a week and not worry about any of this?

Some of us actually travel (like with airplane and stuff), spending weeks (and sometimes months) abroad

I also dislike taking it out when the weather is crap, heavily salty and sandy roads in the winter, heavy rain, etc. It is basically used as a primary long trip and hobby car and secondary city car if and when required.

You think they put them on jacks in the showroom when they spend months there? But they do put them on power supply

[HighlandPete]

Originally Posted by Skyhigh

Another related question - as it is implied, the BMW has some internal protection of the electronics during charging?

Since BMW strongly recommends use of the front connection points for charging and not connecting a charger directly to the battery itself.

From BMW data:

Lead-acid battery, AGM battery:
To prevent the intelligent battery sensor from malfunctioning, use the charging points in the engine compartment.

Only charge the battery via the jump start terminal point. Only then can the voltage supply be registered by the vehicle.

[Skyhigh]

Exactly. That implies some intelligence when it comes to external charging.

Here the setup, just for the sake of it

[Mr Podman]

Originally Posted by Skyhigh

Exactly. That implies some intelligence when it comes to external charging.

Here the setup, just for the sake of it

My 2000 E46 often had a trickle charger on it because it was bad for drawing down the battery.

One item I added to the setup:

A piece of wood (from a German tree of course) placed so the hood of the car cannot be closed 100% at damage the wires from the charger.

podman

[Skyhigh]

Not familiar with the E, but if you don't drop the bonnet of the F but just gently put it down, it does not close completely
Besides that the wires of the DEFA are so thin, that I am quite sure they would not be a problem with completely closed bonnet and cannot get damaged (but I haven't tried). I kept bonnet wide open for the experiment.

[Mr Podman]

Originally Posted by Skyhigh

Besides that the wires of the DEFA are so thin, that I am quite sure they would not be a problem with completely closed bonnet and cannot get damaged (but I haven't tried).

I wouldn't try it.

[Billfitz]

Permanently attach the wire to the under hood terminals, running it to a quick disconnect that extends through the lower grille, zip tied to keep it in place. You don't have to open the hood at all.