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Battery Discharge problem 2nd Question

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A gent called Herbie replied to my 1st question.

So this morning I've got the CTEK MX5 charger.  It says put the black clamp on the car chassis?!?!  not the negative Battery terminal.  I thought my Dad, boyfriends, husband put the black on the neg Battery terminal even when Battery was on the car, that's what I do with the lawnmower.  Is this car suddenly different?  Where on the chassis, the wires are short, the chassis is curved generally.  Need to get this car going been a week now.  Stressed.  What's going to happen if I put the black clamp to the neg Battery terminal?


Thanks in advance again, sorry.

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Black clamp Can go on - ( Negative) Battery terminal BUT Do Not turn On the cars Ignition while the charger is connected and switched On as you may damage the cars electronic components as the voltage output from the Battery charger may go too high (spike).

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Herbie will spot this shortly and can give you a detailed explanation. But in case you're in a hurry, I'll just summarise what he has said in a number of other threads.

Electrically, it makes no difference whether you put the black lead on the Battery negative (sometimes called earth) terminal or anywhere on the car body or chassis. This is because the battery's negative terminal is connected to the car chassis to provide the return route for the electricity rather than having a separate wire to serve this purpose.

The reason it's recommended not to attach the black lead to the Battery itself is because there might be hydrogen gas lurking around the Battery and a spark as you make the connection could cause an explosion. If you connect to some bare metal bit of the car, any spark would be further away from any gas near the Battery. If you have a sealed Battery it's pretty unlikely that there will be any hydrogen and sealed batteries like the AGM type used on many of the Lexus hybrids have a vent to route any hydrogen away from the Battery. Herbie has said in his many years of working with electrical systems he has never heard of an actual explosion.

When connecting jump leads, the recommended order of connection is red (positive) first and black (negative) second. I assume this applies to chargers too. When disconnecting, it's the reverse order. Disconnect black first, then disconnect red. Again, I think this is to avoid sparks.


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