w211 320cdi battery change,advice please

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greasemonkey01

New Member
Joined
Jan 14, 2018
Messages
17
Location
bedfordshire
Car
mercedes c200
hi all,still enjoying the merc but maybe due to being used far less the battery is running down.the car is a 2008 model.i am going to check it out today and if its the original battery i am going to change it.two questions please.is it ok to charge the battery on the vehicle still connected?.if i change the battery will it do what my old 1999 C class petrol did,which was run awfully for 10 miles before the ECU reset itself.any advice would be very much appreciated..
 
I'd only charge on vehicle with a known good charger. Would never connect anything cheap that I did not know was 100% reliable.

When changing just disconnect (neg first off last on) and change.
You'll have to reset windows etc. but that's it, plenty info. on here for that.
 
I've a Trickle charger on my 55, i leave it on there for a couple of days then take it off until needed again 3wks aprox if not been used.
 
My 2008 C220 lives on our driveway and is getting very little use these days, I have a battery condition tester connected and visible through the tailgate so I can see when the battery has dropped to 50%, which ATM takes about 2-3 weeks, I then connect my SIP Chargestar charger direct to the battery and leave it until it completes charging and switches itself off. All works fine so far!

I had a new battery fitted by Halfords in November, it failed in March so they had to replace it under warranty, just disconnected the failed one, hoiked it out (100AH battery weighing about 28Kg!) and put the new one in, leads were only disconnected for about 30 seconds, all worked fine. First change in November they insisted on connecting a small 12v battery to the OBD port "to keep the ECU alive" - big mistake, blew the OBD port fuse (18) and did something to the transmission control module, cost Halfords £174 for my indie to diagnose and fix! Do not connect a power supply to the OBD port!!
 
thanks all for your replies,very helpfull,didnt realise that it would drain down in three weeks .i have a relatively new professional motor trade charger so that should be ok.cars only been used twice in the last month so recharging the battery before replacing it is worth a go.its a mercedes battery on the car.anybody know how to date them.if it is the original one ,i think i will change it as a precautionary measure..
 
Buy one of these (Ultimate Speed Battery & Alternator Tester 6 & 12 Volt Car And Motorcycle | eBay) or similar and use it to monitor battery condition, connect charger when green light goes out and only amber is lit. I'm lucky in that I can rig it in the boot area of my estate, visible through the tailgate, and that when it goes amber I can rig the extension lead and charger onto the battery and then close the tailgate over the extension lead as the big seal round the base of the tailgate absorbs the extension lead, so car can be left on the driveway, charger on but car locked and alarmed. It would be impossible with the SLK with the battery under the bonnet as I would be unable to close the bonnet without cutting the cable, but she's locked in her garage (and SORN'd😰😰) so not a problem.
 

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