Key Fobs & battery life

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RichardSEL

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The fob seems to work fine with the new batteries. So I've no idea what's going on there.

I suspect the cheap sprung tin contacts oxidise and as rust is an insulator start to give low volts to the fob PCB. Mine are discharging down from 3V new to 2.86-ish even after being put in just for a few minutes now. So something's not right.

Random thought for the OP - if bought from eBay etc could be the batteries are fake?

Duracells from Sainsbury £5 for a pair. Can't see any date on the blister pack.
CR2025 and CR2035 seem same diameter - but don't know any difference between their capacities. Was told LED can go leaky although it still lights with new cells in. So took my LED out.
Now fob doesn't even work at all. Waiting on one of the two firms mentioned above to come back with their prices to fix. But guess they can make much more going out mobile to jobs to get locked out Merc owners in! So just a workshop job would take back place...

... because it's not Brexit
 

davidsl500

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Mine had been uncertain to unlock and lock a few times recently so I got some new batteries. They haven't been changed for some years, but I don't use the car much. I was quite surprised that the old ones measured 3V, same as the new ones.

The fob seems to work fine with the new batteries. So I've no idea what's going on there.

Random thought for the OP - if bought from eBay etc could be the batteries are fake?

It's what happens to the voltage in use rather than the no load voltage.
 
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RichardSEL

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2025 and 2035 are differing sizes, one is thicker.

Yes, I assume the CR2025 being thicker has more capacity mAHC

Thanks for the URL for them folks up in Brum -- I did use their site's webmail board to send them a message on Friday, but no reply as yet: "Key Repairs sent by post are £90+VAT, which covers ALL failures with a 12 month guarantee"
 

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I just had an issue with my fob in my 16 year old ML270. Batteries finally failed for the first time. Had to re-establish the connection between the fob and ecu before it would work with new batteries.
Not a bad life for batteries.

Ian.
 
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RichardSEL

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Yes, I assume the CR2025 being thicker has more capacity mAHC

Thanks for the URL for them folks up in Brum -- I did use their site's webmail board to send them a message on Friday, but no reply as yet: "Key Repairs sent by post are £90+VAT, which covers ALL failures with a 12 month guarantee"

I've had a reply from that firm up in Brum who now want £200 +VAT +special delivery to fix my FOB that now (since I took the LED out) doesn't work at all. Originally they were asking me for £250+. I offered to drive up to Small Heath and asked them for a good day for them in case they had to take coding from the car, but no reply to that email.

Thanks for the info on cell numbers: 20mm diameter and either 25 or 32 thick. So am assuming the CR2032 pair would be better for my FOB as that'd give marginally more mAHC? Originally found a CR2025 and a CR2032 in when I first opened the FOB up
 

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So am assuming the CR2032 pair would be better for my FOB as that'd give marginally more mAHC? Originally found a CR2025 and a CR2032 in

I would fit two of whatever was fitted from factory. Too thick a battery could cause issues with shorting on the PCB.
 

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(since I took the LED out)
I saw you said that earlier - why did you take the LED out?

Thanks for the info on cell numbers: 20mm diameter and either 25 or 32 thick. So am assuming the CR2032 pair would be better for my FOB as that'd give marginally more mAHC? Originally found a CR2025 and a CR2032 in when I first opened the FOB up

I'd use the correct size ones - CR2025. On the capacity, are you comparing two of the same manufacturer? They do vary quite a bit depending on who makes them. I wouldn't have thought the capacity was a significant issue as there are other variables which would come into play over the battery's life - how much you use the fob, temperature it's kept in etc.
 
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RichardSEL

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Coz my electronics (from many, many years ago when LEDs were starting to be used extensively) reminded me that some do go "soft" over their lifetime and taking higher than normal current. Someone else asked if I'd tried disconnecting the LED. Which, with this fob that would discharge a pair of new Duracell CR2025s over a period of one month with only every other day use, seemed about right even though the red LED dimly lit. Now it comes on briefly, door locks don't activate either to lock or open, and volts per cell is down to 2.5 or so having had only a few button presses. So am waiting for that outfit in Brum to come back.
 
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RichardSEL

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Stay away from the dealers if you need new batteries. I was charged £7 20 for two Duracell 2025 batteries and got 2 equally efficient Panasonic ones for £4 from Waitrose (£3 60 actually, I get discount at all J Lewis;)) Only takes a minute to change them yourself.

As for batteries not lasting long, I found Keyless Go fobs seem to drain batteries quickly but obviously an R129 isn't affected by this. I'd be interested to know why this is happening too.

Welp, just an update. I desperation went into Merc main dealer spares (if you 'phone them your routed to a 'bot that announces that your call is held in a queue due to the "unusually high number of calls" and you're treated to muzak interspaced with pathetic adverts for stuff you don't want.)

Ten minutes later you're connected to a human who'll only route your call to the "service centre handling your area". And then interrogates you as to why you're calling. Without actually understanding the replies you're giving.

The call get's routed to the number you first dialled (which pretends to be a local number for the local dealership you're trying to call -- its a local shop for local people ;-) and you get thru to a receptionist. Who then interrogates you as to why you're calling. Without actually understanding the replies you're giving. Eventually, you're put through to Steve in spares who says they're not allowed to take an order for a replacement key fob without actually seeing the car's docs, V5, and your proof of ownership. So you agree to drive on over (some eight miles around the south circular for me in slow, slow, stop traffic) Only to be met by a receptionist who then interrogates... erm you get the picture. At that point with temperature rising you ask for Steve in spares to which the receptionist asks which Steve did I want as they've got no Steve Spares working there. At which point I felt as if I was losing my presence of mind and had stumbled into some kind of alternative reality.

With calm precision I ask for Steve - in - the - spares' - department. To which receptionist replies: "Oh, you mean Steve in the parts' department! Won't be a moment, would you like a coffee while you're waiting?" To which I reply that'd be a relief, erm sorry, that'd be nice. "And how do you like your coffee, sir?" Involuntarily, coz I'm being looked after by a shapely young wench of African extraction (but thick as two short planks), I reply: "Strong, sweet, and black. Like my wimmin". Receptionist's radiant smile is replaced by stony glare. What with me being very white an' all. Cold silence follows only broken by the shhhsh-hissss of the coffee dispensing 'bot.

Steve arrives from spares' part's department. "We spoke on the 'phone?" "Could've been," I reply, it was so long ago. Here's all my documents, V5, loads of back MOTs, bill of sale. Steve Parts examines all and announces: "Unfortunately sir, all your documents have the correct VIN number but don't start with WDB. If I put WDB in there then that matches your engine number that's listed on your build record from Bremen. But we're not allowed to issue fresh keys on part chassis numbers without verifying the full number from the engine block first. And that'd be a minimum charge, sir!"

I swallow the last of my black coffee and suppress a choke. "Erm, it's that the batteries only last a few days now before going flat. Can't you copy my existing FOB? It does work." "We're not allowed to do that sir, it's more than my job's worth. But I can fit you another pair of new batteries so you can see how you get on." That familiar feeing of raising blood pressure returns. "Don't worry, they're normally £9 for the pair but I won't charge you."

I agree, Steve Pants, sorry Parts, changes the cells only to find there's two CR2032 in the FOB. And checks that it does work. I drive home (nine miles slow, slow, stop round the south circular) glad not to have been forcably carted away for losing my presence of mind by those nice gentlemen who wear flapping white coats.

They're CR2025. And Mercedes suppies Varta. The fob still works. This morning...
 
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RichardSEL

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That outfit in Brum did get back to me saying that they'd charge me £200 to fix. And if they couldn't fix my existing FOB then I could have my money back. I offered to drive up there from southeast London so they could read from the car's electronics if they could'nt read the key fob / transponder for coding the new fob. But no reply on that.

Another firm at first said they could but then were honest enough to say they couldn't as all Mercedes fobs after 2002 were copy-able, but before that the coding was taken from the VIN number and so would only be Mercedes main agent supply
 

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Only to be met by a receptionist who then interrogates... erm you get the picture. ....

I've likened the reception staff at my local MB to Check point Charlie. I just walk around them now to the parts dept ... very occasionally the service lot. I did once email the head honcho describing them but surprisingly didn't get a reply! :rolleyes:
 
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RichardSEL

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"Every day and in every way, I am getting better, and better, and BETTER!"
(Herbert Lom aka Insp. Dreyfus in The Pink Panther Strikes Again)
 

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Congratulations you have arrived at the MB Total Service Horizon - endless amounts of 'service, sir' but very carefully designed (by experts) to not understand or fix anything.
 
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RichardSEL

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I've been a petrol head since my student days in the '60s (Armstrong Siddley '49MY Lancaster - yes, really!) And progressed via the Rover (four off), VW (two off), Citroen (five off) and Jaguar marques (five off)
Now have Range Rover Vogue, Maserati Quattroporte, and this 'ere SL320 (SLR body converted). And I must say, for a so-called quality product that trades on its past name's reputation, both car and customer service offered is pants IMO.

In both VW and Merc cars you can see the quality that designers tried to impart. Only to be thwarted by cost-cutting numpties who've gone out and bulk purchased cheeep components that'll do the job sufficiently to get customer parted from money and off the forecourt of a dealer.

Met up with an A180 '14MY driver in the motorway services. Showed me a bag of switches that he carries coz the installed keep on failing...
 
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RichardSEL

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It's been two weeks. My fob still works. With those dealer-supplied Varta CR2025 batteries still in it. Innit.

So there I was, in Port of Spain da Trinidad for de Mardi Gras. Coz that's what I like innit...
And she said to me: "Are you a Christian?" I sunk to my knees in front of her and looking up said: "Well, I am now!"
 
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RichardSEL

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It had to happen. Batteries in key fob died. Last used three days ago, so that's about 20 days of life from a new pair of Varta CR2025. One measures 2.13V and the other 2.46V on a cheepo Draper Redline LCD multi-meter.
Replaced with Duracells. Spending out a fiver every 15 days is daft.
Especially since dealership won't sell me a new fob...
<sigh>

I noticed before that one cell of the pair seems to go lower volts than the other for some reason.
They're inserted in the fob one on top of the other with one sprung grab claw connector to the side over the top one (+ve) so you'd think they're in series for a 6V system? That's all I can divine without any circuit
 

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There's a mobile Car electrician (frequently on here) .
based in Carshalton who will supply a new fob for about £140.

Worked for me about a year ago, and no problems since.

If only I could remember his name...
 


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