trickle charging how long?

[Ron07x5]

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?

[bawareca]

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.

[motordavid]

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

[Ron07x5]

Originally Posted by motordavid

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

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

[motordavid]

Originally Posted by Ron07x5

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

Sorry it was unclear...I attach my Battery Tender to the 3 cars and 3 motorcycles, on a regular, rotating basis.

The time it takes to get 'to green' on any of those vehicles is a matter of how long any have 'sat' since I last drove/rode on an extended ride, and how long they have 'sat' with no BTender.

I may leave the BT on for a day, or days, on any given no low or no recent use vehicle, and it simply 'floats' along green for that period. Have never had a problem with extended use or attachment of the BT on any of our stuff, and all 3 Scoots and the Vette have an AGM batt.

That is what I meant by 'floating'.

I read your post of putting your low amp charger on in a couple weeks. I rarely let the cars go that long; they get much more frequent BT charging than a 'couple weeks'...the bikes sometimes get lost in the rotation, and might miss a couple weeks, but not the cars. We simply don't do enough regular long driving, so they get the BT regularly.

Should batts last longer/hold charge a long time? Sure, but they don't seem to these days. So, a BT or charger brand of choice, gets used regularly.
GL, mD

[Ron07x5]

Motordavid did not say I put charger on for two weeks, just 10 to 18 hours. Our use of x5 will be low miles often on level ground. I would like to know if we may deeply discharge the battery this way or not.

So my plan is to manually charge at 1 then 2 and 3 month intervals. If manual charging time increases in like linear pattern then I will know we can face deeply discharging the battery.

I know once a battery has less than 50 percent charge the voltage it provides drops. If lower voltages cause systems to get flaky then I want to avoid that..

Seems nobody really knows what the algorithm of battery charging is so I am left to discover in part by this experimental manual charging.

[motordavid]

Originally Posted by Ron07x5

Motordavid did not say I put charger on for two weeks, just 10 to 18 hours. Our use of x5 will be low miles often on level ground. I would like to know if we may deeply discharge the battery this way or not.

I meant, why wait to 'recharge' for two weeks? Unless it's not convenient, or you are running some kind of test. The low miles/rolling around town may or may not provide for keeping batt charged; in my experience with our cars, it does not. Or maybe it is OK, but hooking up our BT regularly is easy stuff, for 'prevention'.

So my plan is to manually charge at 1 then 2 and 3 month intervals. If manual charging time increases in like linear pattern then I will know we can face deeply discharging the battery.

Batts should go a month or more, and some surely do...my old 'company car' used to sit in airport parking lot(s) for 2 weeks straight, and I never trickle charges those car(s). That was then, this is now, with very different levels of electronics on cars, and maybe different/increased loads and charging req's.

I know once a battery has less than 50 percent charge the voltage it provides drops. If lower voltages cause systems to get flaky then I want to avoid that..

Seems nobody really knows what the algorithm of battery charging is so I am left to discover in part by this experimental manual charging.

Not exactly an EE or Batt xpert here; it is purely anecdotal, but my battery charging regime has worked on my Scoots for 30 yrs, and on our cars for 20 years. Good luck in your test regime, and curious to read an update.
BR, mD

[josiahg52]

My 2011 X5 35d sat for 16 days with the doors locked and alarm armed and it started right up first time. Zero hesitation or drama. I have not looked to see how old the battery is but I got my X5 in November. My driving routine consists of several one to two mile trips a several times a week and a 50 mile trip once every six or seven days. These longer trips are key, I think.

Incidentally, if you want the best battery maintainer, get a BatteryMINDer. I have several and keep them connected to my cars while they are not being operated regularly, i.e., greater than six months, over the winter, etc. I also use them on my spare batteries or other "bad" batteries that other people have given me over the years.

Between my recovery procedures and strict maintenance routine, I have recovered many of these "bad" batteries to greater than 95% reserve capacity. My oldest battery is over ten years old and recently tested over 120% of it's reserve capacity.

It's a hobby and a profession.

[Doug Huffman]

BatteryUniversity.com BU-400 Charge methods

All About Battery Chargers – Battery University

[Ron07x5]

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.