Battery Charging - Disconnect terminals?

[Ponty]

That sounds strange to me. I would think it is the same if you connect the Earth to the battery or the chassis, since they are joined to each other with a strap connector. In all the 50 years I've been charging batteries I've never noticed any difference if I disconnect the battery or not, apart from having to re-set the radio stations.

This is how the manual in my Subaru XV (2019) tells me to do it, as well as the CTEK manual. Disconnecting the battery to charge is a world of pain apparently.

 

[stevec67]

Mine was replaced in November after 11 + years and all local but frequent hops until Covid. They attached a battery to something under the dashboard/steering wheel 'to keep the info. intact' before removing the old and fitting the new. First time I'd seen that.

Quite common these days because so much is coded to everything else and removal of the power can be a nightmare.

 

[dweezil]

This is how the manual in my Subaru XV (2019) tells me to do it, as well as the CTEK manual. Disconnecting the battery to charge is a world of pain apparently.

Mine all have charge posts now so you can attach a 12V source and the battery doesn't make any difference with ignition off.

Used to do a jump lead shuffle in the old days to keep settings.

Big thing on older cars was not to exceed about 17V with a fast starter as that was enough to fry the ECU.

 

[davidsrsb]

Mine was replaced in November after 11 + years and all local but frequent hops until Covid. They attached a battery to something under the dashboard/steering wheel 'to keep the info. intact' before removing the old and fitting the new. First time I'd seen that.

Batteries last about two years in KL. I operate radio base stations with air-conditioning not for the electronics but for the UPS batteries. Lead acid does not like being charged in the high 30s at all

 

[Craig B]

You can leave the terminals on, just make sure you connect the charger to the positive only. The negative should be connected to an earth point on the vehicle and not the battery. This should ensure the vehicle electronics are bypassed. I use a CTEK MXS-10, anything more than 10A is not generally recommended for modern car home charging.

If leaving standing for a while, leave the handbrake off if you can and pump the tyres up a bit.

The suggestion to connect the charger negative lead to a remote earth point on the chassis is a hangover from the none sealed battery days.

I clearly recall my Grandfather removing the caps from both his RV and yacht batteries when putting them on the dumb charger, and instructing me to always leave the hood/hatch open, and to always connect positive first and then connect ground elsewhere (and to always break ground connection first) such that any sparking is remote from the battery.

 

[davidsrsb]

The connect negative last and disconnect first is just precaution against dropping the cable, which will often find something at chassis potential anyway. Drop positive with chassis already connected and you can get melting wire leaping about

 

[sean99]

Many years ago I went to test the voltage on my car battery, forgetting that the multimeter lead was connected to the current input (it so rarely is). It vaporized part of the probe and I was lucky not to be burned. Amazingly the meter still worked after I put a new fuse in.

 

[Craig B]

Many years ago I went to test the voltage on my car battery, forgetting that the multimeter lead was connected to the current input (it so rarely is). It vaporized part of the probe and I was lucky not to be burned. Amazingly the meter still worked after I put a new fuse in.

You definitely know that your battery is a good'un when that happens!

My neighbour/mate James always makes fun of me when he sees me wearing safety glasses whist performing these sorts of tasks in my garage or on the driveway. My reply to him is typically along the lines of; 'I'm glad that you still have eyes to see how much nicer my car looks than yours, my friend.'.

 

[zippy]

I asked a similar question a while ago, when my car was starting to have starting problems due to battery.
The consensus was that it's ok to leave the battery connected while charging, BUT you have to be darn careful not to let any of the bare cable ends touch the car bodywork.
Strangely though, when I have charged the battery out of the car the charge eventually reads 100% and it drops into trickle mode. When I charge with battery still in the car, it never gets to the 100%. I'm guessing that's because something in the car is continuing to draw from the battery - I'm blowed if I can think what as everything (including the alarm) is switched off.

By the way, my car also is a Subaru and disconnecting the battery, as you might expect, causes the electronics to default to 'factory setting' so I had to put the clock right but most other things were fine

 

[Barrymagrec]

In a modern car everything is never switched off.

 

[cctaylor]

That makes sense. Mind you, the risk of sparking is very small and the same with the terminal removed or attached, but I can see why they would go that way.

We had a few electric milk floats back in the day. One very cold winter we used one of the trucks to jumpstart our York engined Transits. They weren't the best at starting when temperatures got much below -5C. Dad and I used 8 or 9 cells giving 16 or 18v. We felt that this was not so hard on the starter as struggling on 12v. Of course you wouldn't want to try that these days with so much electronic gear in any vehicle.

We occasionally had electric float cells blow their top. Typically it occurred when the truck set off first thing after charging. The gas liberated from the overnight charging would be ignited by a spark if cell failed due to old age.