When to use a battery tender?

[Matticus91]

It's a bit late for this trip but I've been wondering if I should grab a tender for some time now. Typically twice a year I'm away for 2-3 weeks out of the country. Is this long enough to need a tender on the battery? I usually drive the car around for a while before parking it for this time, and it's kept in a warm garage so no coldness to worry about.

[WDE82]

I never had problems with my E46 leaving it for a few weeks for similar reasons. Always started right up! It should be fine. I would say get a tender after a month.

But the real decider is what you're comfortable with. A tender isn't expensive, and if $40 gives you peace of mind, why not? It's not hard to hook up.

[Mach1er]

I've read previously that about 3 weeks is the outer safe range for a battery in decent shape at normal temps. I think it might be lower if you have CA and the fob is stored in close-ish proximity to the car. Not certain, though.

[Matticus91]

Originally Posted by WDE82

I never had problems with my E46 leaving it for a few weeks for similar reasons. Always started right up! It should be fine. I would say get a tender after a month.

But the real decider is what you're comfortable with. A tender isn't expensive, and if $40 gives you peace of mind, why not? It's not hard to hook up.

The cost isn't as much of an issue as the setup. I'm in a garage space that I own, but it's a shared parking garage in my apartment building. There's only a few people in my section (6 cars in separate bays) but the nearest power outlet is in the next bay over. I know everyone and they wouldn't have an issue with me using it, but I'd be worried about someone messing with the cord by accident.

[gregthegr8]

Originally Posted by Matticus91

The cost isn't as much of an issue as the setup. I'm in a garage space that I own, but it's a shared parking garage in my apartment building. There's only a few people in my section (6 cars in separate bays) but the nearest power outlet is in the next bay over. I know everyone and they wouldn't have an issue with me using it, but I'd be worried about someone messing with the cord by accident.

You can set it up in such a way that you can basically close the hood all the way and even run the power cord and/or extension cord down through the engine bay and out the bottom, so most people may never notice, though that'll depend on what type you get. Here's an example of someone doing something similar on an M3 with one of the ctek ones, though he ran the power cord over to the side. I think you should have enough room though in the engine bay to hook it up to an extension cord dropped that drops down through some empty space to the ground. The ctek ones also have available extensions for the alligator clips that are pretty long that could help so you can get some extra length if you need. Those extenders cost about $8-10. I'm in a similar garage and have had to deal with this, so I know your pain and having to sweet talk neighbors to use their spaces.

Another option is to leave it, but then hook up the tender/charger for a bit when you get back before you start it up. Easier said than done though if you have to swap spots with a neighbor.

[3002 tii]

Originally Posted by gregthegr8

You can set it up in such a way that you can basically close the hood all the way and even run the power cord and/or extension cord down through the engine bay and out the bottom, so most people may never notice, though that'll depend on what type you get. Here's an example of someone doing something similar on an M3 with one of the ctek ones, though he ran the power cord over to the side. I think you should have enough room though in the engine bay to hook it up to an extension cord dropped that drops down through some empty space to the ground. The ctek ones also have available extensions for the alligator clips that are pretty long that could help so you can get some extra length if you need. Those extenders cost about $8-10. I'm in a similar garage and have had to deal with this, so I know your pain and having to sweet talk neighbors to use their spaces.

Another option is to leave it, but then hook up the tender/charger for a bit when you get back before you start it up. Easier said than done though if you have to swap spots with a neighbor.

That's what I do with my Z. Install in hood, use quick connects and zip tie the little length of wire that hangs to the strut brace fireball pieces. Don't install directly to the battery in the trunk.

[KNS]

I had to leave my 128i for about six weeks (on two occasions), I just disconnected the battery. No problems doing that (left the trunk lid ajar).

[sandlion]

Really? I've left cars for months no problem. Stop overthinking it!

[NorthernDancer]

YES, YES, YES buy and use a battery tender for anything over a week. It can't hurt and it will add life to your battery and we all know how much a new and coded BMW battery is. Its one of those tools you'll have for the rest of your life.
2008 128 still on its original battery.

[champignon]

Originally Posted by NorthernDancer

YES, YES, YES buy and use a battery tender for anything over a week. It can't hurt and it will add life to your battery and we all know how much a new and coded BMW battery is. Its one of those tools you'll have for the rest of your life.
2008 128 still on its original battery.

I have multiple battery tenders for my stable of cars, however you can't be serious when you say it's a tool "you'll have for the rest of your life."

Maybe, if you life is measured in weeks or months, but anything electronic is unlikely to last more than maybe 5 years.

I have already chucked at least one battery tender in the trash, and it was only 2 years old at the time.

[bmw1racer]

Probably overkill, but I use mine every day, since my commute to work is rather short and that's apparently what killed my battery the first time after only 2-1/2 years.

I routed my cable up near the passenger side wiper and have it tucked out of sight.

[tock172]

Originally Posted by 3002 tii

That's what I do with my Z. Install in hood, use quick connects and zip tie the little length of wire that hangs to the strut brace fireball pieces. Don't install directly to the battery in the trunk.

What's the reasoning behind not going directly to the battery?

[3002 tii]

Originally Posted by tock172

What's the reasoning behind not going directly to the battery?

I think even the manual states to charge using the posts under the hood (and not directly connecting to battery). At very least the the negative post under hood is directly connected to chassis but could also have something to do with the intelligent charging system on e9x and later generations (and why you need to code new batteries). End of day hood is more convenient anyway using the pigtails.

[NorthernDancer]

Our dealers here were installing BMW Intelligent Charging System (essentially the 1.5 amp Deltran unit) in all new cars and charging for them. Units were installed in the truck with direct hook up to the battery. So I certainly believe its all a matter of personal convenience. I have 2 cars in storage in my garage-one gets charged via the trunk and the other via the engine.

[champignon]

I have 4 BMWs and 1 VW :-)

All of the BMWs, including my Z3M Coupe, have the battery pigtails attached directly to the batteries with the leads accessible in the trunk. They are all on a charger all the time because I don't drive any of them enough and regularly enough to keep the batteries charged. 3 of them have not been driven in over 3 months given the horrible winter we have had in S. Idaho this year (all have only summer tires). I also put Stabil in the gas tanks for winter storage.

My VW R is the only car I have where the battery is easily accessible, and in this case is under the hood. This car has a negative post that is on the body and labeled for charging or jumping. The negative post is just next to the negative on the battery. On this car I use the alligator clips for float charging.

[WDE82]

Man some of you guys really overthink this stuff...

It's DC power. VERY simple. It doesn't make a difference if you use the under hood posts or put the thing on the battery. It's all in parallel.

[3002 tii]

Originally Posted by WDE82

Man some of you guys really overthink this stuff...

It's DC power. VERY simple. It doesn't make a difference if you use the under hood posts or put the thing on the battery. It's all in parallel.

It's not overthinking, if anything it's the opposite. Use whatever you want, for me the hood is easier to access and has posts intended for this. Am I worried that the battery may explode? No but has it happened to those less fortunate yes lol.

[tock172]

Page 252 of my 2012 135i manual says you can use either the battery posts or the terminals in the engine bay:

Attach the second terminal clamp of the plus/+ jumper cable to the positive terminal of the battery or a starting-aid terminal of the vehicle to be started.

I use the CTEK MUS 3300, which is very similar to the CTEK MUS 4.3, which is actually BMW's recommended charger. CTEK is also a supplier for Alfa Romeo, Chevrolet, Lamborghini, etc.

According to this article, it makes no difference which terminals/posts you use:

http://www.bmwblog.com/2016/01/28/bm...ttery-charger/

One can either connect the battery charger by directly accessing the BMW’s battery through the trunk or via the engine compartment on the red power terminal and the ground.

[gjm120]

If my car is going to sit for 2+ days, I'll put the charger on using the engine compartment. With a good smart charger like the CTEK, it can only defer the day I have to go thru the expense or DIY bother of a new battery.

[WDE82]

Originally Posted by 3002 tii

No but has it happened to those less fortunate yes lol.

Fear mongering. Anyone who's battery exploded had a defective product or wired it wrong. Don't spread wrong information. Like I said, DC power is very simple with just a few fundamentals to understand. The posts under the hood are in parallel with the battery posts. It's equivalent either way.

[3002 tii]

Originally Posted by WDE82

Fear mongering. Anyone who's battery exploded had a defective product or wired it wrong. Don't spread wrong information. Like I said, DC power is very simple with just a few fundamentals to understand. The posts under the hood are in parallel with the battery posts. It's equivalent either way.

Spread wrong information? You act as if I have something to gain by posting what others' experiences are (not mine). Dude I could care less what you do, all I know is there's posts under the hood specifically for this reason. I only tried helping those who asked why I chose to go with the hood route. As I said in my previous post I said the main reason for not charging at the baggery directly was to not mess with the IBS.

[WDE82]

Good info in the images linked. It still would NEVER result in a fire or exploding batteries, but I will agree to recommend under the hood only. I forgot about our car's Irritable Bowl Syndrome since I'm coming from an E46 where that has no effect.