Battery charging in situ.

[CHRISCHANCE]

My ML55 has been parked outside for a few days and though I have never had a problem starting it, I'm wondering that if it doesn't start because of a battery problem; can I connect my battery charger without removing the battery, leaving everything intact?

 

[Monkeylegend]

I leave my SL permanently on an intelligent charger, and have charged with a normal charger, without disconnecting the battery with no issues, I can't see why an ML should be any different.

In fact disconnecting the battery on the SL usually results in a warning message requiring a STAR reset to get rid of it when reconnecting. When changing the battery I connect to an old battery so as not to break the battery connection to the car to avoid this happening.

 

[190]

can I connect my battery charger without removing the battery, leaving everything intact?

Yes provided the battery charger is not an ancient unregulated type. The owners manual should specify the maximum safe voltage which will be something in the region of 14.6 volts. Modern alternators charge at up to 14.6 volts so it must be safe to use a charger at the same voltage provided the voltage is regulated. The danger with unregulated chargers is that when the battery reaches full charge the voltage just keeps going up possibly reaching as high as 16 or 17 volts. If you have a charger with an equalisation mode do not use that mode without disconnecting the battery.

 

[Alex225]

I use a Ctek trickle charger which is designed to be attached to the battery whilst connected. As in I have a pair of permanent leads connected with a socket.

Only issue I had with charging the battery whilst connected was with a jump starter type pack. I was in a hurry to get the car started so tried to get enough into the batter to get it started. I switched the pack to jump start it which in turn damaged the box which the negative of the battery connects to (W211).

Cost me £90 for a used one but would have been £600 if I’d gone brand new.

I suspect that was more the jump starting aspect rather than a trickle charge.

 

[Flyinspanner]

Lidl have an intelligent battery charger, with a jump start facility just about to go on sale. (£39)

With regard to the above, be very careful which mode it's in if you buy one.

Actually - I wonder why it damaged the above, surely 'the box' is designed to have a high current draw through it in normal starting?

 

[190]

Being in a hurry is understandable but charging a battery just enough to get it started is a sure recipe for a short battery life. The idea that the car will then charge the battery fully rarely holds unless the car is going to be driven for many hours. A short commute will categorically not do it. Ideally, if it's going to be charged then charge it fully and remove the charger before starting. Bear in in mind though that a small charger could take several days to fully charge a flat battery.

The thing about equalisation mode is that the charger deliberately charges at 15 volts or more for a limited time in an attempt bring any low cells up to full charge.

 

[BTB 500]

As mentioned any decent 'maintenance charger' will be fine as they're designed to be left hooked up for long periods of time.

My SL is also kept on one of these, again via a socket/flylead that's permanently attached to the battery terminals. As a side-benefit the battery is now 13 years old and still working fine! That alone easily paid for the charger (mine is an Accumate).

Low battery voltage can potentially cause issues beyond simply not being able to start the car ... spurious error codes etc.

 

[CHRISCHANCE]

Many thanks for the response; I've learned something here but pleased to say it was a pleasure this morning as it started as usual with the 1st turn of the key after pulling off 3" of frozen snow. This is a great car but in the 4.5 years I've had it, I haven't seen another - plenty of MLs but no 55's anywhere.
Again, thank you.
Chris.