trickle charging how long?
 

I have a "smart" agm compatible trickle charger. I have used it to maintain the boat battery off season. So I am now running an experiment with the charger on our 2007 x5.

The charger charges at 0.75 amps per hour. The x5 has a 6month old battery installed by bmw. The x5 is driven maybe 50 miles a week unless going somewhere out of town. In last.weeks.we.haven't.used out.of.town.

So the charger has a red led meaning I am charging and a green it.is charged led. So far we have gone 10 hours for a total of 7.5amps in and it is still showing it.is charging. So how long til it show fully charged how many total amps in?

So one.would think it should have topped off the battery by now? But I have read about these cars losing battery charge over time especially with short to the store trips and especially with the twin turbo v8s. True? Note this one is a non turbo 4.8 v8

So opinions? comments?

So the charger should put in 24 x .75amp hours per day = 18 amps per day. The battery should be 90 amp hours battery so a impossible completely empty battery would charge in about 5 full days.

On would figure the battery should have more than half charge and.I would hope 3/4 or more so one.would.figure in a day or.at.most.two it.should.show fully.charged.

So here is a question if my battery is 20 percent low now what stops it from going lower and lower til it is out of juice? Can this happen with design of the charging system in these cars? Should I put the trickle charger on it maybe once a month to avoid the possibility of flaky things from a discharged battery?

Following the huge problems with high current usage when car is not in use (that means that it didnt go to sleep mode fully, not that it has a high sleep mode current) with the 7 series E65 and early 5 series E60, BMW implemented some extra functions. If the car was supposed to be in sleep mode, but it continues to draw high current, most of the consumers will be shut down and only a few will be left "armed", CAS and a few others. This function will prevent the battery to be drained completely, but it may stay at a low level of charge without giving some noticeable clues for the regular owner. With DIS and ISTA an "Energy Diagnosis" menu can be accessed where all random wake-ups and other energy related events are recorded.

Not an exact comparo, but our '01 3.0, with a 2 month old newly installed batt, may take up to a solid 'overnight' to get back to green using my ol'Battery Tender.

This comes after some up and down our mtn/local driving. Same goes for our '02 Vette.

The arithmetic is nice but most good low amp chargers don't 'lie', and it takes what it takes to get back to green. Otoh, once up to green, it floats along nicely and barely comes on again, with charger in place.
GL, mD

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Battery tender went to green after charging for between 10 to 18 hours. That might mean the battery was 10 to 15 percent discharged.
I will try charging again in two months if the percentage is the same or less then it is no concern. If the percentage rises it will then be worth trying again in 4 more months.

Question is how discharged will the battery become over what time period.

What do you mean by floats along nicely and barely comes on again with charger in place? In place when and where?

I have a AGM battery in our E53. Not sure whether the E70 comes stock with a standard lead battery or AGM.

Every 2 months or whenever I remember, I will put our chargers on it, mainly because AGM's are supposed to be charged up to 14.7 versus a traditional battery, 14.4. Whether those .3 volts is a big difference on whether these AGM's sulphate or not, I don't know. I just try to be proactive about it...