[JFP]

Can you or can you not charge a battery that is connected in the standard manner i.e. must you always disconnect one of the terminals before connecting a battery charger ?

 

[pete_turier]

I would say that you'd be OK leaving the battery connected, provided you switch the charger off at the mains before connecting/disconnecting. There is a (very)slight chance of causing a voltage spike if the battery is connected, that's why manufacturers tell you to disconnect the battery. However, I've been a mechanic for nearly 25 years, and I've never seen any damage caused by this!
Pete.

 

[900016Turbo]

Most "Trickle" chargers purchased for charging car/boat/caravan batteries have smoothing circuitry in-built so it really shouldn't matter what order you use to charge that battery.

I have knocked up a variac transformer which I can set between 0 & 100 volts & more importantly, 0 through 30 amps. On the odd occasion when I've had to chatge a flat battery, I have left it connected in the car & quick-charged at a rate of about 10 amps at 14 volts. Throwing this kind of charge into a battery means that the battery needs assistance in breathing else the pressure can & has blown off the screw-down tops over each of the six internal 2 volt cells. I can charge a totally flat battery like this & it's capable of turning over & starting the car in under 10 minutes. That's the kind of power that I'm putting into the battery.

This kind of charge will never completely charge a normal lead/acid battery. As the battery becomes charged, the amperage needs to be dropped to "fill" that battery to a fully charged state. (Think of it like trying to fill a glass with water from the tap with the tap on full bore. You'll never completely fill it. You have to slow the rate of charge to get the last few drips into the glass. So why am I telling you all of this?

A battery that is being charged at this rate produces a lot of gas. This gas is highly flamable. Under these circumstances, I would always switch off the variac before disconnecting the leads from the battery terminals as to not do so will always result in sparks being produced as the charging circuit is broken. The last thing anyone would need is a battery that explodes as the gas ignites discharging battery acid everywhere. Including me! Imagine the mess of your engine bay & then your face!!!

If you've one of those standard trickle chargers that can only charge at a traickle, then there's definitely no need to disconnect the battery from the car.

Hope this answers your question.

 

[Zaphod Beeblebrox]

I would always disconnect the battery terminals, for the simple reason of the possibility of damaging some delicate electronics. All for the sake of less than a half minute's work.....

 

[Paul D]

Interesting feedback, and Pete's experience is worth noting.

There are trickle charge devices, such as photocell panels, which plug into the cigarette lighter socket and trickle charge the battery whilst in situ.

But, unless you do not have the radio code, or wish to loose ECU fault data (etc), I would disconnect the live lead off the battery before connecting a standard charger, on the basis that 'if accidents can happen, then they will happen'!

If the charger lead became disconnected and then retouched the batter terminal, the resulting voltage spike could 'potentially' damage some expensive electronics.

 

[JFP]

Thanks for the info.

The reason I asked was that i'm not using my AERO much at the moment due to having to drive a Ford Focus company car.

I've got a battery ''conditioner'' for my motorbike and was wondering whether i could connect this to the car (via some fixed terminal and connector block) or whether I would have to disconnect the battery each time