Battery charging on car
myke pocock - 13/3/24 at 05:05 PM
I have a 2016 Ford Kuga. Is it acceptable to disconnect the positive terminal from the battery, connect the positive lead from the battery charger to
the post and the negative lead from the charger to any earth point on the car? Reason for this is the negative battery post is virtually impossible to
get to without removing the battery and that's a total pain in the butt.
gremlin1234 - 13/3/24 at 06:37 PM
modern fords use a battery monitoring system in the neg lead.
I suggest NOT disconnecting the battery, but just charging via the chassis connection point near the battery, and the 12V terminal on the battery
itself.
if you do disconnect the battery many things may have to 're-learn' - which can be good for clearing codes etc,
but can cause issues with auto gearboxes, (robot clutches), and issues with things like windows up/down limits.
Slimy38 - 13/3/24 at 08:52 PM
I'm sure the current thinking is to connect the negative lead to the body anyway? My Skoda Superb actually has a covered bolt attached to the
chassis that is specifically there as a negative charging point, it has no other purpose. Positive connection straight on to the terminal.
As Gremlin says, don't bother disconnecting the battery as there's no need and certainly a lot of downsides.
Just to check, does your Kuga have start/stop? Those systems require AGM batteries which in turn require specific battery chargers.
falcor75 - 14/3/24 at 06:47 AM
Removing the positive terminal instead of the negative can cause eletrical issues. Always remove the ground post if needed.
To charge the battery you dont really need to remove either of them.
Mr Whippy - 14/3/24 at 10:30 AM
As above, you can just charge it whilst fully connected, there is no risk. The charger will only see the voltage across the battery (otherwise it
would be discharging all the time) and the charger will probably raise the voltage to around 14-15 volts which is just what the car does normally when
its running.
I have trickle chargers on the cars and lawn tractor to keep them topped up, I use Halfords "advanced 1A smart charger" which is really good
value @£25 and does a range of voltages, it comes with a simple plug to connect permanently to the battery terminals.
[Edited on 14/3/24 by Mr Whippy]
coyoteboy - 14/3/24 at 02:28 PM
quote:
Originally posted by falcor75
Removing the positive terminal instead of the negative can cause eletrical issues. Always remove the ground post if needed.
To charge the battery you dont really need to remove either of them.
Exactly what do you think removing the positive will do wrong?
Why would anyone remove the positive terminal while charging anyway?
I'm confused. Just plough onto the positive terminal with it attached and connect to the block anywhere.
craig1410 - 15/3/24 at 09:57 AM
quote:
Originally posted by coyoteboy
quote:
Originally posted by falcor75
Removing the positive terminal instead of the negative can cause eletrical issues. Always remove the ground post if needed.
To charge the battery you dont really need to remove either of them.
Exactly what do you think removing the positive will do wrong?
Why would anyone remove the positive terminal while charging anyway?
I'm confused. Just plough onto the positive terminal with it attached and connect to the block anywhere.
The biggest risk of removing the positive lead (with the negative still connected) is that the tool used to remove the post nut/bolt might touch the
chassis and cause a big spark, shower of molten metal and potentially a fire. The same risk is not present when disconnecting the negative post first
(assuming it's a negative earth vehicle of course). Of course, if the tool shorts across the battery terminals themselves then it doesn't
matter which end you remove first but you can mitigate this risk easily by keeping the positive battery terminal cover in place until the negative is
removed. Then cover the negative battery terminal with a cloth or something while removing the positive.
But as others have said, it's preferable to charge most modern cars with all terminals connected. The car user manual will probably provide
guidance on where to connect a charger or jump leads too.
Mr Whippy - 15/3/24 at 11:20 AM
Don't worry, there's no molten metal just some hefty sparks. Been there done that more times than I should, it does wake you up though 
But your totally right that is the reason for removing them in that order and it has nothing to do with protecting the electronics which does not care
less which end is disconnected. It's also the very reason for putting fuses on the positive side (as close as possible to the battery) since once
it's gone to earth, everything metal is a wire to the battery.
However just to put a spanner in the works, my old car is a positive earth yeah I do have think about what I'm connecting up...
I was told that the reason for the preferred negative earth was it was found to help reduce body corrosion in salty conditions.
craig1410 - 15/3/24 at 11:49 AM
quote:
Originally posted by Mr Whippy
Don't worry, there's no molten metal just some hefty sparks. Been there done that more times than I should, it does wake you up though
But your totally right that is the reason for removing them in that order and it has nothing to do with protecting the electronics which does not care
less which end is disconnected. It's also the very reason for putting fuses on the positive side (as close as possible to the battery) since once
it's gone to earth, everything metal is a wire to the battery.
However just to put a spanner in the works, my old car is a positive earth yeah I do have think about what I'm connecting up...
I was told that the reason for the preferred negative earth was it was found to help reduce body corrosion in salty conditions.
Well, sparks are molten metal but anyway, whether you get small sparks or bigger blobs just depends on the size of the battery versus the size of the
metal object shorting it out. The battery in my 5 series is something like 900A CCA and I imagine short circuit current is a good bit higher than
that!
Biggest shower of sparks I ever caused was when I tried to jump start a car under sodium (yellow) street lights where red and black look very similar!
I had the good car engine running (bit silly) and was just connecting up the jump wires but somehow managed to reverse the polarity. Frightened the
bejesus out of me but thankfully didn't damage either car. My jump leads were a bit the worse for wear though! Since then I've always
followed the rule of connecting up the positive lead first at one end then the other, before connecting up the earth lead to the good car and finally
the earth lead to the flat car but not directly to the battery. You're supposed to connect to the chassis or engine at least 30cm away to
minimise the risk of igniting hydrogen from the bad battery. Not a big risk outside on a windy, rainy night though which in my experience is always
when you have a flat battery!
Yes, negative earth was introduced to reduce corrosion, I can confirm that story.