Changing the battery

[Uky]

This is the advice that I got from a friend who works as a prefessional MB Mechanic.
If the battery is bad but not "gone". (It may not apply to yours but changing a 212/207
main battery is not specifically difficult.)

Open the hood.

Open the driver side door.
Down the window.
Close the door but do not lock it
with the remote (or keyless).
Remove all keyless keys well out of range.
Place the normal key out of reach.

Wait for ~20 - 30 minutes. The vehicle should be in sleep mode by then.

Replace the battery, (-) first and last.

(While you are at it, there is most likely a bunch of old leafs under the battery plate
so it could be removed and the area underneath cleaned. Be careful: One of the bolts
is quite short as it is right above one of the AC refridgerant hoses. Make sure you
replace that very bolt with one with same length! (On my 207, those bolts seemed to be
semi-self-tapping. I had to replace all of them)

If the 207/212 has been properly in sleep-mode, there should not be any need
for recalibration. I replaced the VRLA-battery in my 207 following the procedure above.
No problems.

(The opening of the door and window down is just in case something happends with the remote. If that happends, you will be able to get in and drive.)

 

[14emerc]

Just a quick update 14emerc. Just had a look in WIS & there is no mention of having to calibrate the battery after replacement so maybe on Mercs you don't have to do this?

Well, that handy, one less thing to do!

 

[14emerc]

This is the advice that I got from a friend who works as a prefessional MB Mechanic.
If the battery is bad but not "gone". (It may not apply to yours but changing a 212/207
main battery is not specifically difficult.)

Open the hood.

Open the driver side door.
Down the window.
Close the door but do not lock it
with the remote (or keyless).
Remove all keyless keys well out of range.
Place the normal key out of reach.

Wait for ~20 - 30 minutes. The vehicle should be in sleep mode by then.

Replace the battery, (-) first and last.

(While you are at it, there is most likely a bunch of old leafs under the battery plate
so it could be removed and the area underneath cleaned. Be careful: One of the bolts
is quite short as it is right above one of the AC refridgerant hoses. Make sure you
replace that very bolt with one with same length! (On my 207, those bolts seemed to be
semi-self-tapping. I had to replace all of them)

If the 207/212 has been properly in sleep-mode, there should not be any need
for recalibration. I replaced the VRLA-battery in my 207 following the procedure above.
No problems.

(The opening of the door and window down is just in case something happends with the remote. If that happends, you will be able to get in and drive.)

The process you have listed will come in handy and it makes good points to consider when replacing the battery. I have to say, getting to the bolt that holds the battery in place, is and could be tricky and care must be taken not to drop the 13mm bolt down the side of the engine! I can imagine that even greater care will be needed when refitting.

 

[14emerc]

The section below is from here: How To Charge an AGM Battery - Hot Rod Magazine

'Here’s all you need to do: Grab another car battery with a decent charge on it (12.4 volts or better) and connect it in parallel to the problem battery using a set of jumper cables. Then activate the charger and charge the battery normally, being careful to follow the manufacturer’s instructions for current and voltage limits. It’s as simple as that. The second battery supplies the voltage that tricks the charger into supplying the necessary current. After an hour or so, you can remove the second battery and continue charging. We tried it and it works. No matter how deep the discharge we applied, we were able to bring the battery back to a full state of charge using our cheap but trusty bulk charger.'

Well Markjay, did have ago at your idea. I found some old but still in good condition jump leads and used the new battery that was just delivered, bang on time and at a good price. I started by topping up the new battery via the charger to ensure it was at max. Then connected the jump leads +to+ and -to- . Left it like that for an hour and then got a reading of 11.8v on my volt meter on the old battery. Having disconnected the jump leads I then connected the smart charger and the old battery started to take a charge as you and toolman said it might once the charger see some volts above 10ish.

 

[14emerc]

Ok, so the battery has been refitted. Got to say that it's a bit of a fiddle getting it back into the correct position. I kept the battery terminals covered until I was ready to reconnect the leads, in the correct order. The holding down bolt and plate are not easily seen and thus not easily got at. With the battery In place, and it's worth just ensuring that it has seated flat and not lipping on the battery plate, as you can't see to ensure its not lipping. Once happy the fun of fitting the securing plate and holding down bolts starts. With the plate in place, i held the 13mm bolt in place in the socket with a bit of tape. I used a 1/4 drive extension anything bigger will be very difficult as there is so little room down the side of the battery. Having now reconnect the leads I needed to resynchronis the windows. I also turned the steering wheel each direction to the max. Reset the electric wing mirrors and that was about all. Thanks to all who took the time to post me "pointers" much appreciated. Pete

 

[David404]

...Handy also to have a small multimeter to keep your eye on the voltage. Normal caveat about no smoking etc etc when charging a battery applies.
Another top tip from "my house and garage is full of rubbish ".Steve

If you use an old charger best to disconnect the battery from the vehicle. Old chargers can put out too many volts which can damage cars electronics.

 

[190]

MB specify a maximum safe charging voltage of 14.8 volts. Any charger old or new that exceeds that voltage is unsafe to use. Old chargers tended to be unregulated and the voltage could rise well above 14.8 volts when the battery was approaching or had reached full charge so they certainly could damage the cars electronics.