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Author Topic: Merc 2 battery question.  (Read 8200 times)

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Merc 2 battery question.
« on: 16 July 2017, 07:44:08 »
From time to time I like to codition charge my car battery to try and keep it in tip top condition.

The Merc has 2 batteries, one undr the bonnet and one in the boot.

There is a dedicated charging point under the bonnet for attaching  the + and - clamps from the charger.

Question is, does the charger then try to charge both batteries at the same time?

If it does, I can't see how it could go through the conditining cycles :-\
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TD

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Re: Merc 2 battery question.
« Reply #1 on: 16 July 2017, 08:15:07 »
The 'charging points' I think are for jump starting .... if you have a look I believe they will have gert big cables to them  :)

I would have thought the 'charging points' are connected to the battery connected to the starter only.
The other battery being a separate circuit for running electrics and gets charged from the alternator only....
« Last Edit: 16 July 2017, 08:18:37 by TD »
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Re: Merc 2 battery question.
« Reply #2 on: 16 July 2017, 08:25:35 »
Quote from: TD on 16 July 2017, 08:15:07
The 'charging points' I think are for jump starting .... if you have a look I believe they will have gert big cables to them  :)

I would have thought the 'charging points' are connected to the battery connected to the starter only.
The other battery being a separate circuit for running electrics and gets charged from the alternator only....

According to the manual they are charging/jump starting terminals.

The + goes straight to the + on the battery under the bonnet and the - goes straight to ground on the body.
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TD

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Re: Merc 2 battery question.
« Reply #3 on: 16 July 2017, 08:50:40 »
Quote from: Auto Addict on 16 July 2017, 08:25:35
Quote from: TD on 16 July 2017, 08:15:07
The 'charging points' I think are for jump starting .... if you have a look I believe they will have gert big cables to them  :)

I would have thought the 'charging points' are connected to the battery connected to the starter only.
The other battery being a separate circuit for running electrics and gets charged from the alternator only....

According to the manual they are charging/jump starting terminals.

The + goes straight to the + on the battery under the bonnet and the - goes straight to ground on the body.

So, be fine to use for charging then  :y

My other point about the other battery being on a separate circuit still stands, having them connected in parallel all the time makes no sense to me...apart from looking at a wiring diagram I guess the other way to prove its separate, is to disconnect the + from the one in the boot and see if the lead still has 12v on it....
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Re: Merc 2 battery question.
« Reply #4 on: 16 July 2017, 09:14:15 »
Quote from: TD on 16 July 2017, 08:50:40
Quote from: Auto Addict on 16 July 2017, 08:25:35
Quote from: TD on 16 July 2017, 08:15:07
The 'charging points' I think are for jump starting .... if you have a look I believe they will have gert big cables to them  :)

I would have thought the 'charging points' are connected to the battery connected to the starter only.
The other battery being a separate circuit for running electrics and gets charged from the alternator only....

According to the manual they are charging/jump starting terminals.

The + goes straight to the + on the battery under the bonnet and the - goes straight to ground on the body.

So, be fine to use for charging then  :y

My other point about the other battery being on a separate circuit still stands, having them connected in parallel all the time makes no sense to me...apart from looking at a wiring diagram I guess the other way to prove its separate, is to disconnect the + from the one in the boot and see if the lead still has 12v on it....

Disconnecting batteries on a Merc can lead to all sorts of problems, so I'm lead to believe :(
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Re: Merc 2 battery question.
« Reply #5 on: 16 July 2017, 09:21:20 »
Are you SURE that there is a direct link to the under-bonnet battery, with no big fat diode or relay in the line?

Ron.
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Re: Merc 2 battery question.
« Reply #6 on: 16 July 2017, 09:33:29 »
Quote from: Bigron on 16 July 2017, 09:21:20
Are you SURE that there is a direct link to the under-bonnet battery, with no big fat diode or relay in the line?

Ron.

Yes :y
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Re: Merc 2 battery question.
« Reply #7 on: 16 July 2017, 09:36:15 »
Quote from: Auto Addict on 16 July 2017, 09:14:15
Quote from: TD on 16 July 2017, 08:50:40
Quote from: Auto Addict on 16 July 2017, 08:25:35
Quote from: TD on 16 July 2017, 08:15:07
The 'charging points' I think are for jump starting .... if you have a look I believe they will have gert big cables to them  :)

I would have thought the 'charging points' are connected to the battery connected to the starter only.
The other battery being a separate circuit for running electrics and gets charged from the alternator only....

According to the manual they are charging/jump starting terminals.

The + goes straight to the + on the battery under the bonnet and the - goes straight to ground on the body.

So, be fine to use for charging then  :y

My other point about the other battery being on a separate circuit still stands, having them connected in parallel all the time makes no sense to me...apart from looking at a wiring diagram I guess the other way to prove its separate, is to disconnect the + from the one in the boot and see if the lead still has 12v on it....

Disconnecting batteries on a Merc can lead to all sorts of problems, so I'm lead to believe :(

Maybe  :-\

Tho if you use the merc fairly regularly on decent runs and its not parked up for a week or two at a time, if it were myself, I don't think id bother to charge the battery  :-\
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Re: Merc 2 battery question.
« Reply #8 on: 16 July 2017, 09:40:40 »
Right I think I have answerd my own question.

The battery in the boot is a small 12v.

The battery  under the bonnet is a big starter battery.

Both batteries read different voltages.

If they were linked in any way, they would read the same voltage :y
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Bigron

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Re: Merc 2 battery question.
« Reply #9 on: 16 July 2017, 09:49:14 »
Is the boot battery voltage lower by about 0.7 volts than the larger battery?

Ron.
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Re: Merc 2 battery question.
« Reply #10 on: 16 July 2017, 11:22:56 »
Ahh, the joys of start-stop wank ;D
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Re: Merc 2 battery question.
« Reply #11 on: 16 July 2017, 11:25:12 »
Not sure if the Merc is the same, but on the Shaguar, you have to be careful where you connect the charger due to the battery monitor "ecu" on it.  Plugging the charger directly on the battery terminals confuddles the hell out of it, then it does all sorts of weird shit, like not charging the battery when the car is running.

Don't ask how I know this ::)
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Re: Merc 2 battery question.
« Reply #12 on: 16 July 2017, 11:30:05 »
Also, TB, if you use a conditioning/maintaining charger - the Halfords "smart" charger, for example, you can potentially (no pun intended!) confuse the ECU because it pulse-charges, and they don't like it up 'em!  :(

Ron.
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Re: Merc 2 battery question.
« Reply #13 on: 16 July 2017, 11:31:05 »
I just don't get any of this. I've had my astra for over two years now, never felt the need to go near the battery, it just does everything it needs to do by itself. If it went flat for any reason, then I'd know it was kaput and fit a new one.
Why the need to charge the battery on your cars?
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Re: Merc 2 battery question.
« Reply #14 on: 16 July 2017, 11:46:45 »
The need arises when you leave it unused for a week or two, due to the quiescent drain taken by all of the splendid systems incorporated into these modern Omegas.  :-X

Ron.
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