Battery.

[roadtripper]

AGM batteries are built better than standard lead acid batteries. They should take discharges better as well. That said, Discharging to the point it will not start or so low car functions do not work does permanently take some capacity from the battery. Shortly after a long drive I checked my battery voltage and it was 12.6vdc. I expected higher because of the long drive. I started the car and the voltage went to 12.8vdc. Again, I assumed it should be much higher like 13.4-13.8. Our batteries are in the car not under the hood like most cars. I wonder if the under charge the battery to reduce off gassing? Shouldn't be much of a problem anyway since its a sealed battery.

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[John8]

AGM batteries are built better than standard lead acid batteries. They should take discharges better as well. That said, Discharging to the point it will not start or so low car functions do not work does permanently take some capacity from the battery. Shortly after a long drive I checked my battery voltage and it was 12.6vdc. I expected higher because of the long drive. I started the car and the voltage went to 12.8vdc. Again, I assumed it should be much higher like 13.4-13.8. Our batteries are in the car not under the hood like most cars. I wonder if the under charge the battery to reduce off gassing? Shouldn't be much of a problem anyway since its a sealed battery.

BMW only charges to 80%. When my battery is charged it goes to 12.6 to 12.8. It is charged, so it drops the voltage, that is normal.

 

[roadtripper]

John, I understand what your saying. However the lower voltages are not normal for other 12volt vehicles. Are all BMW's like this?

 

[John8]

John, I understand what your saying. However the lower voltages are not normal for other 12volt vehicles. Are all BMW's like this?

Mine charges to 80 to 82%, and this is normal for BMW.

 

[roadtripper]

If a battery is overcharged it will fail prematurely. If a battery is undercharged it will fail prematurely. Our batteries are AGM batteries. It would take me hours to fully explain battery charge state and charge stages. BMW does not design and manufacture batteries. The people that do this recommend charging an AGM battery to 13.6 to 14.6 volts. even though a fully charged battery is 12.6-12.7 which is a stable voltage meaning battery left to rest for a few hours. Bringing the voltage up temporarily to 14.6 volts reduces sulfating which kills a battery. So what I'm saying is our batteries will not last the 6-8 years I'm accustomed to. Your Arizona heat will destroy a battery even faster. I am going to have a conversation with my battery and tell it that BMW has it's own laws of physics and it needs to change the way it works.

 

[puzzled]

A member PM'ed me about the Battery Tender I had been using on my cars including my Supra so I'd thought I would post here as well for anyone interested. Seems to work just fine.

It's the small JR (750mA) version per below.

https://www.amazon.com/gp/product/B000CITK8S/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I found that the parking brake pulls a lot of current. If I just park without the parking brake usually it will go into float in less than an hour. If I use the parking brake, it can charge for hours. That said, I stopped using the parking brake in my garage. It's an old habit since I drive mostly MT cars..........

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