mikapen

I want to disconnect my battery to install external charger pigtails. I am purchasing a 9 volt Memory Saver from NAPA so my ML doesn't lose its mind. It plugs into a 12V socket.
Multiple questions: Is 9v sufficient for the computers on a 2010 ML350 BlueTec?
Does the ignition need to be switched to the 1 or 2 position in order for the 12V socket to connect? Is one socket better than another?
It looks like the 12V socket in the passenger footwell is usually hot (unless it has gone to sleep, I guess - 4 days?) Would that work better and not require the ignition switch?

lkchris

There aren't any usually hot sockets.

I'm also not certain that leaving the ignition switch on will do any good as probably nothing is direct-wired to that, i.e. wired via relays other devices, etc. It may in fact be detrimental to disconnect battery with switch on.

Don't think you can expect to "save" any settings and recommend you simply read your owners manual under "battery--disconnecting." This isn't as difficult as you imagine.

mikapen

Thanks for your thoughts. I know the owners manual cautions about disconnecting the battery with the switch in the '1' position, but for most cars that does not apply if you provide back current through a 12v socket. If the socket is controlled by a relay, then the back path is clear unless there are diodes in the circuit.

The owners manuals have been "dumbed down" in the last couple of years, so my '10 manual probably keeps more secrets than your '07. I wish that weren't so, but that's why I am posting.

My manual does mention three things that must be re-syncronized after removing power - windows, sunroof and mirrors. If it were just those I'd be OK, but I am pretty sure there are other things that must be synch'd again - I know about the power steering, I think there is climate control, and I can only guess at what else. I am trying to avoid being surprised when I don't need a surprise.

I think back to the time my C240's sunroof wouldn't stay closed when I was outside a hotel during a snowstorm. I behaved like it was sensing a "pinch" and kept backing off. All it needed was to be syncronized, but I had no clue at the time.

Another thing that will present a problem is that I can't figure out the sequence of removing plastic covers around the seat rails and battery, in order to expose the negative terminal! That's certainly not in the owners manual....

Vernl

It might be easier to attach your ''pigtails'' to the ''boosting'' points under the hood. No need to disconnect anything then.

lkchris

All very true but the fact remains there is ZERO need for any of it.

Just disconnect the battery, do your installation, reconnect and resynchronize as specified.

sosh

By using that device you are putting some rather expensive electronics at risk. I would forget your memory saver and just re set all that needs to be reset,

mikapen

Thanks for your replies. Where does this all lead me?
First, I think the 9v "memory saver" isn't a reasonable solution. I am not sure what the MB service centers use as substitute power during battery swaps, but I think they use 12 volts. I now think that newer MBs and Chryslers need 10.8v to keep their electronics awake.
So, I'll abandon that idea.
This leaves two choices: 1. Either connect the "pigtails" to the jump-start terminals while everything is hot, but just be careful. (Those terminals or the fuse box are my intended locations in any case).
Or 2. Disconnect the battery, do it right, and live with resyncronizing whatever is needed - the three I know about, the two I suspect (steering & climate) and maybe more.
The "disconnect" method still leaves me with not knowing how to access the negative battery terminal to disconnect it, with all the plastic covers, seat mounts and carpet pieces to remove in some kind of sequence.
I am leaning toward the riskier #1. I have done that many times with only one mistake, which wasn't very expensive - a length of wire and a melted screwdriver.

Vernl

You do realize it's no different hooking to the jumper posts, than hooking to your battery, even if your battery is disconnected, it can still jolt you if you short it out.Your battery tender pigtails are insulated and have covers on the disconnects and I really dont see a way of shorting out while hooking to the under hood points. I hooked up mine in less than 5 mins under the hood without disconnecting the battery, tie strapped the pigtail along the right side and can plug it in in 30 seconds and not have to worry about closing the rear door on my charger cable all the time.

mikapen

Sorry if I confused you. That's what I was talking about from the beginning.
I should have broken my post into two or three topics, so folks wouldn't have to read between the lines:
1. Should I use a 9v Memory Saver if I disconnect the battery on a 2010 ML BlueTec;
2. How do you get to the battery in a 2010 ML BlueTec;
3. What needs to be syncronized after disconnecting the battery on a 2010 ML BlueTec, beyond the three things mentioned in the 2010 Owners Manual?

I had already decided on my location for the pigtail - similar to the five cars I have Battery Tenders installed. 1st choice: the underhood fuse box, 2nd: the jumper points. The fuse box would result in cleaner wire routing but there is the danger of a momentary "open" and flashing the electronics.

Thanks to all your posts, I have ruled out the Memory Saver. For now, I have ruled out trying to get to the battery because of the unknown (to me) sequence of removing bits and pieces that hide the negative terminal.