Short term storage

    for the last 26 years i just use a battery trickle charger 

     this year i have gone HI TEC and got one of these from maplins (i think)

      not big bucks and a nice long lead 

     and leave the hand brake OFF 

     had no problems at all

I have a 2006 S500 so some of it's idiosyncrasies might also apply to your G.

First off, it doesn't like being parked for as long as 3 months.

My car has 2 batteries, one is just a starter battery (used obviously just for starting the engine) the other runs all the computer stuff and over 3 months this is likely to drain and the computer stuff doesn't like being without power. It results in problems with various ECUs and on the occasion that I did allow this battery to drain meant a computer re-set at a MB dealer.

Definitely don't park for 3 months with the handbrake on. Mine also prefers to be parked in N rather than P for any extended period (obviously only on level ground).

That's a lot of weight to be sitting on those tyres for 3 months - although as Adrian says above, he hasn't had any problems and he stores his G for much longer than 3 months every year.

If at all possible I recommend having someone prepared to start, run and drive it once per week. Avoiding problems is much cheaper and less frustrating than fixing them.

Sorry, got confused and thought you had a G300E. However, the 320Cdi is not as complicated as the later,  W221, S500, so I think that it will be fine to disconnect the battery. You will afterwards need to reset the electric windows (open and re-close fully once) , sunroof (ditto) and possibly the ESP (turn steering from lock to lock) after reconnecting the battery. The 2007 G still has the body electronics introduced in 2001. My 2001, G400 Cdi is quit happy with battery disconnection.

I don't know whether you intend to leave the vehicle in your garage, on your drive or on the road, but I certainly would not leave it on the road unattended for this length of time.

Ideally, if stored in a garage, you could use a CTEK charger:

http://www.ctekdepot.co.uk/

To be proper anal i would leave it on blocks with wheels off the ground

Dis connect battery and it will be fine if it,they are in god shape

If its damp push pads off discs and clean discs before use again

I have seen many cars left standing with the pads on disc and it causes rusting and future issues

It all depends on the humidity of garage

I also give the engine a spray of wd 40 as leaving any used car standing sometimes causes hassles

Yes to my first part about having wheels off ground just helps tyres and bearings sitting in one place for 12 weeks

I have never had any issues at storing cars outdoors or garaged using the above

I never use a charger just in case anything went wrong and it over charged or cooked itself. Modern electronics are good but a disconnected battery is safer in my own view

A friend had an expensive optimate type charger on his bike and it failed and cooked battery

I just disconnect and re set clock and job done

I was not going to say but a lot of cars that i look after have stood all winter. Brakes are a bit siezed but now i have brake judder. Its where the pads have sat and contaminated disc. I wont be told different i have seen it 100s of times before. Just spin wheel and clean discs but if you have pushed pads back a little bit you wont have an issue. Dont forget to press pedal a few times to get pads back to disc or you wont stop lol

                                             G In depth report

It will be just fine

Have a good trip

Perhaps you may consider using a solar panel charger if practicable.  They are very low amperage but sufficient to trickle charge the batteries.

Another point to consider is to over inflate the tyres so that they don't create any flat spots,

I leave my car regularly for prolonged periods with the battery connected  and I only had a battery problem once.But this was an 8 year old battery.  For as long as  the battery does not fall below 12.5V it soon recovers. 

Although I do not know for certain, as current flows from the battery, it should allow flow back to the battery; I cannot image a restricted reverse flow from the adaptors, it goes against cost effectiveness under current Mercedes production costing logic. 

I think you can trickle charge.

Thanks again Arnie.

I know my Smart car is only active when the ignition is on. But will have a look for the under bonnet connectivity. I was looking for a battery...

All those symptoms are normal for a low battery. If the voltage drops below 8,5 volts, the electronics will complain.

However, I would advise to change the battery ASAP, if you intend to use the car, as continued charging and starting attempts could result in more serious faults.

Modern cars continue to draw power when the ignition is Off, and will discharge a battery in a month or two. So for long term storage leave a trickle charger connected, or disconnect the battery. Once a lead- acid battery has been fully drained and left like that, it will never recover fully. if the battery is older than 5 years it may be best to replace it.

Tanya batteries (on line )  have good prices on Varta Silver series batteries,  with delivery.