[ty666]

I've been getting a battery discharged warning every time I turn the car off during the past couple of weeks , (the weather has been cold) -10 to -20 celcius. I've been using the battery tender plus charger, i keep it plugged in over night for a couple of nights, then the next day I drive the car, I got the same warning message when I turn the car off. Now I'm wondering if the charger is actually doing it's job properly.

Charger should display a solid red light while charging but under 80%, a flashing green light while charging but over 80% charged & solid green light when fully charged (in storage). I've been checking on the charge status several times a day & I've never seen it flashing green meaning over 80% & charging. I keep checking & it's either solid red or solid green. At one time after it was solid green (therefore fully charged) I disconnected the charger for a second & then connected it back again & the light turned back to solid red (meaning it's charging & the charge is less than 80%) it stayed red for a few hours until I checked again the next morning & it was solid green again. I find that if the battery started accepting charge a second after it showing that it was fully charged (solid green) that the light should've at least turned to flashing green as the battery should have more than 80% charge.

Is there anything wrong with my charger? anyone else experienced this as well?

[ajob]

What's happening doesn't sound right.

Two things to start with:

1. Make sure you attach the charger at the dedicated +12V charging terminal in the engine compartment. If you attach it at the battery terminal or, worse, plug it into a cigarette lighter, the car electronics will react unpredictably.

2. Make sure the charger is set for an AGM (absorbed glass mat) battery type, used by all modern BMWs; these batteries have a slightly higher final charge and maintenance voltage. If the charger doesn't mention AGM somewhere, it may be of the wrong type for your battery.

If you have access to a multimeter, check and write down the battery voltages, maybe your tender has gone bad.

If you look to buy a good new one, I can report that since many years I'm using an 8 Amp C-TEK charger/tender, same maker of the (costlier) BMW branded chargers; it's sold online.

[ty666]

Originally Posted by ajob

What's happening doesn't sound right.

Two things to start with:

1. Make sure you attach the charger at the dedicated +12V charging terminal in the engine compartment. If you attach it at the battery terminal or, worse, plug it into a cigarette lighter, the car electronics will react unpredictably.

2. Make sure the charger is set for an AGM (absorbed glass mat) battery type, used by all modern BMWs; these batteries have a slightly higher final charge and maintenance voltage. If the charger doesn't mention AGM somewhere, it may be of the wrong type for your battery.

If you have access to a multimeter, check and write down the battery voltages, maybe your tender has gone bad.

If you look to buy a good new one, I can report that since many years I'm using an 8 Amp C-TEK charger/tender, same maker of the (costlier) BMW branded chargers; it's sold online.

I borrowed another deltran battery tender plus charger from a friend to try it for a couple of days. it says on the charger that it's suitable for AGM batteries (but has no option to choose a specific type) so I guess it's made to work with AGM as is.

I don't have access to a multimeter, however I have this aftermarket headup display. I use it mainly to project my speed on the windshield as it's easier than looking at the instrument cluster.

https://www.amazon.ca/Susenstone-Uni...9&keywords=hud

And this has an option to show battery's voltage, it's plugged in to the car's OBD port. Normally it doesn't turn on until I turn the car on, however when the battery tender is plugged in, the HUD turns on (even with the car locked) & instead of displaying speed (as I set it up) it dsiplays the battery's voltage.

Voltage has been fluctuating between 13.4 & 14.7 (when the charger is red & charging, voltage is in the 14's, when the it's fully charged/green, voltage would go down to the 13's) which I can't make any sense of it as I don't know what it means anyway. LOL

Charger is connected directly to the battery in the rear. I was reading today that It's better to connect the charger to the front near or else I'd risk decreasing the life of the battery. For the time being I won't bother switching as it's too cold & I don't feel like spending 15-20 minutes outisde in the -20 C to switch it to the front. Anyways my battery is 4 years old, so if I won't complain if I had to replace it next winter.

[LondonF33]

Never attach it direct to the battery. The car controls the amount of charge from a tender only from the from charging terminals. You need to switch it ASAP as otherwise you aren't going to get this solved and you may damage the battery.

4 years is a good run for a car that may not get much use however try it like I said and you should be ok.

[Almaretto]

The other thing you can try is running battery test in ISTA+.
If battery was not registered when put in vehicle, that could also cause issues.