OEM BMW battery vs third party

[lyunardo]

Hey, now that it's getting cold the battery in my 02 Z3 3.0i is draining really quickly.
If it sits for 3 days the battery will be about 7 volts.
It's not even really that cold: 40s and 50s in the day, mid-30s at night.
It may be time for a new battery, which is fine. But I'm thinking I might be better off with a high quality 3rd party battery instead.
What I have now is part #61 21 2 353 806.
Any thoughts?
Thanks,
L

[BimmerBreaker]

Any battery that meets the correct specs is fine to use

[Tigershark48]

Another one of those items that’s priced all over the map. Agree, it’s all about specs. The most expensive isn’t necessarily the best.

i was fortunate. While scheduling pickup from the out of state dealership on my newly purchased roadster, they discovered the battery was nearing the end of its life. They promptly put a brand new 5 year warrantied battery in on their dime. Nice.

[Vintage42]

There are many batteries that meet specs.
BMW battery 61 21 8 381 738
Duralast Platinum H6-AGM (AutoZone, comes with vent hose)
Interstate MTP-H6 Megatron (NAPA)
Sears DieHard International Gold H6 AGM
Walmart Ever Start MAXX H6
Pep Boys Bosch Performance #48 H6
AutoCraft Platinum H6-AGM

But they all need to be tended through long periods of inactivity in the winter climates.

[Tigershark48]

Agree. Running a Battery Tender Jr. during winter layup.

[Dakar Ole]

I think it best to go dealer battery. My last one went 11 years. The new dealer one is made in Austria and was only marginally more expensive than third party. Of course no fitment problems.

[Tigershark48]

11 years is pretty sweet. What was the cost of the battery?

[Dakar Ole]

The battery was $165.74 on 11/9/17. They carried it to my car, I popped it in and they took the old one away. The quality of a BMW battery is nothing to snicker at.

[Tigershark48]

Hopefully the same source for my 2017 BMW motorcycle.

[daven]

Dealer replaced my original battery after 3 years. Since then it has been on a tender if parked for more than 4-5 days. It lasted 11 years. I replaced it with a Autocraft Gold 48H6 from Advanced Auto and its now going strong after 5 years. It was a little short so I put a folded paper shim between it and the hold down strap. I'll tell you in another 6 years if it beats the oem.

[fmcfad01]

I've had the Autocraft ones in both of my cars.

M Coupe must have a short somewhere as it's killing batteries. I need to go mess with it and my multimeter...

[Adker]

I did some research into batteries when I put up some solar panels. Want the battery to last longer, some suggestions.

Buying the proper size battery limits the amount of discharged during starting. All batteries have a limited number of charge/discharge cycles.
Keeping them charged increases life, batteries discharge while not in use.
Keep the battery charged, they do not do well when deep discharge. See curve below. Overcharging will also damage the battery so use trickle chargers when stored.
Some batteries are built better then others. Deep discharge batteries are built to resist the effects of deep discharge but cost more $$. Normal auto batteries have a good life for the money.
Heat reduces life, not much you can do about this if you live in a hot climate.
I tend to buy batteries from the same manufacturer if they last. Sometimes you just have to buy what is available for a reasonable cost.
Cost.... no matter how much you pay, they will go bad over time. I get about five years out of Auto zone batteries in my cars and the replacement cost of keeps going up!!!

[Tigershark48]

Good information. Any idea what percentage of charge they lose just sitting, as in storage month to month?

[MartyBtoo]

I always love battery discussions. In my prior life I was in charge of a Telco central office, which had an AGM battery bank that was 6'x6'x40' in size. All AC coming into the facility was converted to 48VDC and fed into the battery bank, which supplied all of the telco equipment and ran inverters to provide all of the AC for cooling systems, etc. Nothing was directly powered by line AC. The rooms that had electronics in them were kept at 62 degrees, but the battery room was kept at 80 degrees. One time the main AC transfer switch fried, so we didn't have access to either line AC or our backup generator. That battery plant put out over 1400 amps of 48VDC for over 12 hours before they were able to get a new switch installed and operational. Now that's a battery!

Marty

[Adker]

Good information. Any idea what percentage of charge they lose just sitting, as in storage month to month?

Good question, I have never seen a spec on a battery for self discharge rate. I suspect it is related to how well the battery is maintained charge/discharge, the quality of the lead and acid solution and general construction of the plates and interconnects. I did a quick search and found this chart for power sonic batteries. Appears if you store the battery in below freezing conditions, the discharge is really low. There is a discharge amount (right side of chart) were the battery may fail to fully recharge.

http://www.power-sonic.com/images/po...hManual-Lo.pdf

[Tigershark48]

Very neat.

My attached garage, where my cycle and car are stored, stays anywhere between 40 and 55 degrees F throughout the winter. Your chart tells me it would be 6-10 months before the battery would require charging to start the vehicle. As long as it gets charged before starting the car, it shouldn’t experience any damaging extreme discharge rate. Based on that, I personally don’t need to trickle charge it over winter. Since it’s a brand new battery, that would definitely apply this winter. I have my tender on my motorcycle and planned to swap it back and forth with the roadster, but it looks like I don’t need to do that.

The cycle is a 2017, so it probably does not need trickle charging over winter either. If we have one or two perfect days to ride, I could just put the tender on the night before, so it’s at 100% when I start it.

Please correct me if I’m wrong.

[Adker]

The curve is from one manufactures batteries, results could vary. You also have to consider the current draw from the cars systems. You could disconnect the battery to eliminate that draw. You also might want to make sure the battery is 100% charged before storage and before first start. If you can run a cord outside, a small 12V solar panel works well.

[Tigershark48]

Good point. Anything is possible including a very low level short somewhere, how much the clock draws, etc.

To chart this myself, do I need more than month to month voltage change?

[Adker]

Once a month should do. You will have to take accurate voltage reading, the difference between a charged and uncharged battery with no load is a little over 1.5 volts.

[Tigershark48]

How does the voltage drop correlate with the percentage capacity chart you show? For example, at 9 months at 50 degrees? I’m trying to understand how I could accurately build the same type of chart for my stored roadster.

[Adker]

Look at the pdf link, figure 5, open circuit voltage. The rate looks linear with a no load voltage of 11.5V for discharged and 13V for fully charged. I suspect the fully charged voltage will change a little from battery to battery depending on manufacture and health of the battery.

[Tigershark48]

Thank you sir. I missed the .pdf link before. I’ll study the entire .pdf to try to get more up to speed. I looked at figure 5 and that appears to tell me what I need to know to track the unloaded discharge rate over time monitoring voltage during my storage period. If I have more questions, I’ll let you know. I intend to track it weekly for the month of January. If the loss is as minute as expected, I’ll extend measurements to monthly through the rest of the winter layup. I’ll post my findings this Spring. I also plan to pull the tender off my motorcycle and document the storage discharge rate the same as the roadster. I’ll skip riding it this winter on any surprise perfect weather days to complete the study.

Fun stuff.

[lyunardo]

Thanks for all the recommendations and advice.
I think my OEM battery is still good.
I usually keep my Battery Tender plus on my motorcycle this time of year.
Before posting this, I had put it on my Z3 to bring it up to 12 volts and then drove it around for a while. Apparently that wasn't enough.
This time I left it on until the meter showed 14.4 volts, and wouldn't go any higher.
Since then, it's holding a charge normally, and not draining between drives.
L

[Randy Forbes]

If you have a Tractor Supply Co. (TSC) in your town, their Schumacher tenders are very inexpensive and seemingly indestructible; I've got five or six (5-6?) of them to cover my own cars and the occasional long-term customer's car.

A few years ago they went through a design re-engineering, that reduced their weight considerably, probably from a XMFR to inverter-type technology (?) but I've yet to have either type fail and they're in use 24/7.

I don't think I've ever paid more than the $20.00 they're on sale now for either; good value and negligible investment (Christmas Stocking Stuffer candidate...).

https://www.tractorsupply.com/tsc/pr...a?cm_vc=-10005

For convenience, Amazon has them (duh...) for only a few dollars more.

https://www.amazon.com/Schumacher-SC...=1545142365117

[Tigershark48]

Can’t beat the price.

Do you hook up directly to the battery in the trunk, or to the jump terminals under the hood or do you take the battery out of the car?