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Discussion Starter · #1 ·
Hello Everyone, how long can I leave my 2018 GLC 250d 4matic without starting it? I have to travel for approximately 9 weeks. The car is garaged. Will the battery be flat when I return? Are there any steps I can take to reduce the battery usage while it is in the garage? Thank you. Chris
 

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Hi,
Unless you got someone in your household to start your car for at least 5 to 10 minutes every week. Other wise you can buy a battery charger that you can leave charging the battery without overcharging.Check your local auto shop .
Hope this helps
Cheers
 

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Modern cars don't really sleep, sensors are continually checking the condition of the car and, of course, the anti-theft systems require constant power. I doubt your battery will cope with 9 weeks of constant drain. Starting it weekly and letting it tick over of a short period in the garage is likely to escalate your problem. Diesels have a high compression ratio so will pull a huge amount of amps out of the battery to fire up. It is unlikely the alternator would be able to replace that loss, especially with the engine just running at idling speed. I suspect around 4 weeks would be the maximum duration for an unassisted start-up. Battery performance drops off as the temperature goes down and even a healthy battery will deliver less "cold cranking amps" in winter so warming the battery with a fan heater to nearer normal room temperature will improve the chance of starting. Beyond 4 weeks the voltage across the battery may have dropped beyond the threshold set by the engine management so you may find it throws up fault codes. I'd connect jump leads to another vehicle with a known good battery before attempting a start beyond 4 weeks.

Of course the proper way to lay up the car would be to connect an intelligent/smart battery charger which continually monitors the condition of the battery and charges it accordingly. Not sure of your location but if you are in the UK, have a look at this CTEK charger for just under £60:

 

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Modern cars don't really sleep, sensors are continually checking the condition of the car and, of course, the anti-theft systems require constant power. I doubt your battery will cope with 9 weeks of constant drain. Starting it weekly and letting it tick over of a short period in the garage is likely to escalate your problem. Diesels have a high compression ratio so will pull a huge amount of amps out of the battery to fire up. It is unlikely the alternator would be able to replace that loss, especially with the engine just running at idling speed. I suspect around 4 weeks would be the maximum duration for an unassisted start-up. Battery performance drops off as the temperature goes down and even a healthy battery will deliver less "cold cranking amps" in winter so warming the battery with a fan heater to nearer normal room temperature will improve the chance of starting. Beyond 4 weeks the voltage across the battery may have dropped beyond the threshold set by the engine management so you may find it throws up fault codes. I'd connect jump leads to another vehicle with a known good battery before attempting a start beyond 4 weeks.

Of course the proper way to lay up the car would be to connect an intelligent/smart battery charger which continually monitors the condition of the battery and charges it accordingly. Not sure of your location but if you are in the UK, have a look at this CTEK charger for just under £60:

CTEK MXS 5.0 Automatic Charger
nothing to add
 

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Discussion Starter · #5 ·
Toobad, thank you very much for your comprehensive reply. You certainly covered the spectrum of possibilities. One last question I have is whether I could disconnect the battery before leaving the car since it will be locked up in a garage and can be left unlocked? Would this help? And are there any implications to disconnecting the battery? Chris
 

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I'd do what Toobad suggests and invest in an intelligent charger, I'd have doubts about disconnecting the battery, maybe you should ask the advice of your dealer.

I've no experience of leaving my GLC for extended periods however have done so on 8 occasions with several cars for periods of 5 and 6 weeks at a time while on long haul holidays.

These were Minis (petrol), Audis A4 and A6 diesels a BMW 320d and a VW T5 diesel van. All were left on the driveway, several times in winter weather and every vehicle started without issues.
All the cars were under 2 years old, high spec and likely to draw as much current while dormant as the GLC. The VW van was 4 years old but with tracker and alarm system drawing power.
 

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I would caution you against disconnecting the battery for the 9 weeks you are away. Theoretically the worst that will happen is the inconvenience of asking MB Assist to call round and reinitialise the engine management computer via the car's OBD socket. More worryingly is the fact you will have £40k+ of uninsured vehicle sitting in your garage for 9 weeks. Your insurance premium has been calculated on the basis your car has a certain level of security provided by the manufacturer. Without a battery connected you run the risk of invalidating your insurance and having any claim refused.

Sounds like you could be potentially heading for a world of pain and I would positively encourage you to invest in a charger. It would leave you worry-free and extend the overall life of the battery to boot.
 

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Thank you for all the information. I was having a warnings with my GLC battery because I don't use it every day and just purchased a CTEC MXS 5.0 to keep it topped up. It mentions the time taken to 80% charge depending on the battery size (Ah); e.g. 2Ah 2h, 8Ah 8h, 20Ah 4h, 60Ah 12h, 110Ah 26h; but I can't find the battery spec for my 2016 GLC 250 D 4matic sport premium. Can anyone advise me please?
 
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