Battery tender for agm battery via jump posts advised?

[andrewwynn]

Measure current on the starter. The draw can go up more than 100A as starter wears out. I've been meaning to get some baseline values I'll see if I can do that soon.


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[andrewwynn]

I wouldn't even consider non AGM. I also buy at Sam's club! Saved me $70


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[omodos]

I been meaning to take and leave it at an auto electrician but cant function without the x daily....amp draw test on cranking with clamp used at rear batt cable showed 392 and up...so on one hand yes at 5 years old batt is ageing on other 392amps even for a split second is high apparantely at startup

[omodos]

Originally Posted by andrewwynn

I wouldn't even consider non AGM. I also buy at Sam's club! Saved me $70


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Haha thanks for tip fella if only i was in the U.S....am on that tiny island in the eastern mediterranean ....mail order shipping stuff in is prohibitively expensive...waiting for a price for an agm now...will post here when i get it and you will keel over when you see price....

[EODguy]

What about a solar battery maintainer that has a cigarette plug? Mounted in hatch back window and plugged into the always on rear socket? Bad, good, okay?

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[omodos]

Got one plugged into the front lighter socket...so i.am on borrowed time with current battery...having to charge it more often means its lost its original capacity...thanks for feedback

[andrewwynn]

It's not as drained as you think. Here's the problem: if you have a 12v battery and 0.015 Ω resistance in the cable and connectors you will get 9v to the starter if there is 200A draw at the starter. That's ok because the starter would be designed to operate at 9V (they still call it 12v) I can assure you zero percent chance the starter ever gets 12v while cranking.

Now: change nothing but the starter draw and use 400A. 0.015 Ω x 400A is now 6V loss on the wire and you will get only 6V to the starter when cranking.

I think the normal draw is 200-250A for E53 depending on number of cylinders and if it's diesel.

I've been seeing a lot of posts where people replace battery and alternator when it's really the starter that has failed.

To put things into perspective and put an exclamation point on keeping contacts clean: a high quality switch contact or plug-in pin socket is typically between 0.005 and 0.010 Ω. Basically this is why a loose battery terminal is a disabling event. It could be 0.1 Ω which means at 200A you would lose 20V (of of 12) and the high resistance contact if the battery could push the full current would be 20V · 200A = 4000W which would quickly destroy the contact.


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[Crowz]

This is how I added a charging port to the E53.



Magcode Connector | Crowz Nest

I use solar panels to charge it when it isn't driven much. Which was often when it was mine. After being evicted from it and forced into the E70 it never sits anymore as the wife drives it daily so the charging port isn't really used anymore for now. But it works flawless when needed

[andrewwynn]

Where did you put that? It's a work of art. Since you can just use a 12v outlet that stays live it's over kill. Beautiful Overkill


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[jsoto]

I've run $350 + higher end AGM batteries. Even in the E53. Currently running a wet cell.

IMO, AGM is worth it if one deep discharges it (in this age of ED, AGM is a must). Or concerned about long term storage, discharge factor if not in a batter minder.

On the flipside, AGM is very sensitive as battery charging voltage and if you may have weird alt issues, those will reflect downstream on your battery whereas a Wet Cell can take some voltage burps. Just my 2 cents

Now that more vehicles demand AGM due to start-stop charging profile, AGM's have become a bit cheaper