"Low Battery, Please Start Engine" message....

Faults and Technical chat for the Discovery Sport
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Badgerface
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Re: "Low Battery, Please Start Engine" message....

Post by Badgerface » Fri Jan 11, 2019 12:44 pm

Just a quick input - when I had the pleasure of Land Rover Assist to my house one Sunday morning last year, the technician connected Red lead to Positive battery terminal, and Black to the far left of the engine block on the nut at the top of the mounting itself.
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Re: "Low Battery, Please Start Engine" message....

Post by Mamil » Fri Jan 11, 2019 12:54 pm

Badgerface wrote:
Fri Jan 11, 2019 12:44 pm
Just a quick input - when I had the pleasure of Land Rover Assist to my house one Sunday morning last year, the technician connected Red lead to Positive battery terminal, and Black to the far left of the engine block on the nut at the top of the mounting itself.
Was that for a jump-start Badgerface?

The instantaneous current flow in a jump start situation can be in the hundreds of amps, and can damage the sensitive BMS which is attached directly to the battery negative terminal, so it's best to have the negative lead attached far away, such as the chassis ground point you describe. That way the circuit is from the donor battery positive to the starter motor, and back through the chassis and the negative wire to the donor battery. The high current path bypasses your battery and BMS so is less likely to damage it.

However, when charging the battery as geonic was asking about, you are trying to push current into your battery, but only about 5-10 amps maximum will flow, which is well below the normal amps flow when the engine is running, so it's quite safe to attach the charger negative lead much closer to the BMS. In fact as I mentioned above it's quite important to the sensing mechanisms in smart chargers that they are attached as close to the battery terminals as possible, or under/over charging can result..
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Re: "Low Battery, Please Start Engine" message....

Post by geonic » Fri Jan 11, 2019 1:11 pm

Thanks Mamil for your explanations!
This encourages me in giving a new battery a try and hope that the BMS will recalibrate itself re. learn the values of the new battery shortly.

Anyway, I will try charging with the negative attached to a chassis ground point first. My charger Optimate 6 is limited to 5 amps.
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