[Tambohamilton]

Hey all, got a not e9x but closely related question for you...

Getting battery discharge warnings on my partner's 2009 e81 118d. It has the original 80AH AGM battery.

Voltage at the jump start terminals with nothing on (no lights etc) is 12.35v.

Voltage at the battery posts, with the trunk/boot interior light on is 12.2v. This also measures the same at the jump start terminals, with the trunk light on.

Voltage with the engine running at idle, and only the interior lights on, is 14.8v at the battery posts and jump start terminals.

New battery time, or something else?

Thanks.

[TunafishE93]

Your voltages are below 50%, charge up and see if it holds 12.8V AGM or 12.6V standard. Alternators are maintainers not chargers, if you hold a charge than problem solved.

Or due to age you can just get another, 11 years is a good run. It is your battery though.

[Tambohamilton]

Yeah, I've charged it recently and it's gone back to this state. That said, I didn't actually check the voltage it reached after charging. I let it run overnight (12h+) on a 5A smart charger, so I think it would have had enough time to reach near full charge. That was about a month ago.

Honestly, I think it's about done. It's done a decent innings. I just wanted second/third opinions before I drop £ on a new batt.

Thanks for the suggestion

[gbalthrop]

Originally Posted by Tambohamilton

... 2009 e81 118d. It has the original 80AH AGM battery. Voltage at the jump start terminals with nothing on (no lights etc) is 12.35v. Voltage at the battery posts, with the trunk/boot interior light on is 12.2v. This also measures the same at the jump start terminals, with the trunk light on...

If you are wondering if that "Voltage Drop" is excessive, why not calculate total "Wattage" of bulbs lit with boot open, and then do similar test (same ~ wattage load) on YOUR car. My SWAG would be that is NOT unreasonable Voltage Drop for several 5W to 10W bulbs.

Also you do NOT indicate under WHAT Conditions you get "Battery Discharge Warnings". If you only see a yellow battery voltage warning light after turning engine off and continuing to use electrical consumers such as radio, then that is NOT of itself indicative of anything significant AFAIK. If you have INPA or ISTA, check Power Module for Battery SOC & SOH records in the Histogram.

Personally, I would do NOTHING more than simply identify the best replacement battery & source, so you are prepared to swap when it fails to hold a charge overnight, or flunks the Starter "Load Test" (goes to ~ 10.5V when measuring Voltage at Jumpstart Terminals, AFTER applying starter Load (NOT during application of load). Carry Jumper Cables (and know how to use them ;-) just in case.

WARNING: I'm a "Bottom-Fisherman" and YMMV.

Also, I have a 2/10/50A charger/jumpstarter and I live < 10 minutes from a Walmart that carries Auto Batteries and is open 6AM to Midnight EVERY Day, and have an alternate vehicle to pick up a replacement on ZERO notice. So when it comes to batteries, I'm NOT big into "Preventive Maintenance."

George

[Tambohamilton]

thanks George. You sure do live in a handy place for having an unreliable battery!

The excessive discharge warning generally happens on a cold (~5degC) morning, when the car is started. I don't think it triggers when the key is inserted; I think it's when the starter is engaged.

The error code for excessive discharge (see below) seems to be persistent though, and doesn't clear using Protool. The rear demister doesn't work now, for example - I'm assuming it's been disabled to conserve power.

I'd sort of like to follow your idea of waiting for it to properly die before replacing it (getting ALL of my money's worth), but the chances are when it dies it'll strand my partner and our 2YO son somewhere, and that wouldn't make for a fun day.

Thanks for all the input so far!


Protool error codes:
KOMBI [KOMB87] | A559: Dashboard: Voltage supply has been switched off (standby current cutoff relay)

Only other code I'm seeing is A6D1 from the JBBF, which relates to the aux water pump. I'm guessing it's just worn brushes, and already have replacement brushes handy for the fix....when I have time.

Edit:
Also I don't really think 0.2v drop is crazy to light a ~10w(?) bulb, though I'm sure a new battery would fare better, I just mentioned it because I wasn't going to disconnect the trunk light just to match the voltage at the jump start terminals.

[Efthreeoh]

The battery is 11 years old almost? It's worn out and not holding a charge. Just get a new battery.

[porsche959]

10 Fukin years . R u serious

[Tambohamilton]

Originally Posted by porsche959

10 Fukin years . R u serious

I know it's an old battery, but that alone doesn't mean it's dead (yet). Hence asking for opinions

[e90yyc]

Originally Posted by Tambohamilton

I know it's an old battery, but that alone doesn't mean it's dead (yet). Hence asking for opinions

^ Yup.

When I replaced my battery at 165,000 miles, I couldn’t believe it was still on the original battery. It lasted over 11 years in a bitterly cold climate. Impressive.

For all the headache it can cause, the IBS does an astonishingly good job of optimizing battery life.

[Tambohamilton]

Nice! This one is at 100k miles in the UK climate (never very cold, never very hot). I'm sure it'd help life expectancy if the car was primarily used for long trips, which this one certainly isn't any more...

[Tambohamilton]

Originally Posted by porsche959

10 Fukin years . R u serious

Maximum troll. Made this comment then voted to check something else. Muppet.

[Efthreeoh]

Originally Posted by Tambohamilton

I know it's an old battery, but that alone doesn't mean it's dead (yet). Hence asking for opinions

I've had a few batteries last longer than 10 years. The one in my '99 F150 lasted 14 years and the truck sat most of the time as I used it mostly on the weekends it's entire life. While it was still turning over the engine, when I finally swapped it for a new battery, it fired the engine far more faster.

I also have a 1999 Honda motorcycle with a 1,500CC flat six, so basically a small car engine in it. While I keep the bike on a battery tender, the original battery lasted 15 years; in heard of for a motorcycle. Again it was slow cranking the engine and a new battery was a vast improvement.

So I get the "is it really the battery" question.

But car batteries, especially in an E9X, are constantly being cycled. The best I've gotten out of my E90 as far as battery life is 6 years and my car is driven almost 4 hours a day at two stints of 2 hours each. Lose the alternator in an E9X and you'll get about 25 miles out of it running on just the battery.

A car battery with 10 years on it is statistically near or at its end-of-life. Battery chemistry changes over time. BMW batteries live in a bit better environment since most are located inside the cabin in the trunk, away from heat and vibration, but because it is a chemical process, the battery eventually just wears out. There really is no point in trying to see if there is a fault in the charging system as a first order of diagnosis when the battery is 10 years old. The first order of diagnosis is just replace the battery with the correct sized replacement and then determine the health of the charging system. At 10 years old, there is not much life left in the battery anyway.

If the battery were new, or just a few years old and working fine, then suddenly starts to fault, then that is when you look to the charging system first.

My 2 cents.

[Tambohamilton]

Good input, thanks for that. I'll get a new battery! I have no real reason to suspect anything else is failing, so that seals it that I should just get a battery and hope that's all it is.

[Tambohamilton]

New battery in today, coded (upgraded to 90AH AGM, because it was cheaper!?), registered, and VO updated. Letting it charge overnight tonight, even though it was reading 12.8v out of the box, just to be sure it's starting its time in the car at 100%. Let's see how it goes...

[Explorerlyon]

Originally Posted by Efthreeoh

I've had a few batteries last longer than 10 years.

Have you stayed with a particular battery brand for those years and all your vehicles? Or, are you diligent about keeping your batteries charged and that contributed to the long life?