A basic (perhaps even stupid) question - Anglesey Ian
I know that shrugged shoulders of despair will result,but please sympathize and indulge me by answering these questions:

Can the battery on my Saab 9.3 Tid be charged (with a mains operated battery charger) in situ whilst still connected to the electrics ?

Apart from the radio code, do I need to be aware anything else if the battery is disconnected: ie will the ECU and other electronic gubbins reset itself etc ?

With thanks in anticipation

A basic (perhaps even stupid) question - pettaw
I THINK so, provided the voltage doesn't go over 14.5-15 volts with the charger connected I don't see the harm that could result.
A basic (perhaps even stupid) question - Aprilia
Yes and no! It depends on the charger.

Some just contain a transformer and bridge-rectifier circuit - these can hit batter with well over 18V - they may damage the car's electronics if left connected. The more modern chargers (like the Gunsons 'Gold' autocharger) are strictly regulated and will not overcharge the battery or damage any electronics.
A basic (perhaps even stupid) question - Peter D
Hi, Assuming you are just charging the batter with 3 or 4 amps for a couple of hours then the current falls off to 2 or lass amps then it is perfectly safe. If you like measure the battery voltage after a couple of hours and it should about 14.25 to 14.75 depending on the quality ( i.e. ) age and condition of the battery Regards Peter
A basic (perhaps even stupid) question - Robin the Technician
Hi Ian,
It is always recommended to charge a battery with it disconnected from the vehicle. You can have problems with radio bulb failure and sometimes damage to other electronics in the vehicle. The usual failure to occur is reversal of the diodes in the alternator which can be mighty expensive. I ALWAYS charge a battery off the vehicle on a trickle charge for a minimum of 24 hours.

Hope this helps

These are the views of Robin the Technician with 35 years in the trade. I fix, therefore I am...
A basic (perhaps even stupid) question - buzbee
always recommended to charge a battery with it disconnected from the vehicle:

The fag of putting codes back in etc., is always a temptation to risk a charge in situ, as I have done sucessfully many times in the past. My cum-uppance came as a shock with one of my cars that got a flat battery that was actually caused by going near open circuit. Modern batteries, you never got that in the old led-acid days!

Putting on a standard charger put 18V or more on the system electrics and I was lucky to avoid a large bill as a result. There were a few noises and I yanked the leads off quick. So what I do now is to try putting the headlamps on. If they show a substantial light, I know the battery is already passing a substantial current and unlikely to be damaged by a few amp charge.

But it would be expensive and so sometime I must get one of those voltage limited chargers. What do they cost ?
A basic (perhaps even stupid) question - RogerL
On a modern vehicle, if the alternator and battery are in good service condition, the battery shouldn't need charging. If it does either the alternator or battery or both need attention. Continued recharging of the battery is not the answer to this problem.

Find out whether the alternator or battery or both has a problem and fix that problem. Good auto-electric outfits are useful here.
A basic (perhaps even stupid) question - Anglesey Ian

Can I thank one and all for your kind guidance and advice in answering my query.


A basic (perhaps even stupid) question - buzbee
On a modern vehicle, if the alternator and battery are in
good service condition, the battery shouldn\'t need charging::

Whilst this is largely true, the modern car still takes a small current from the battery while standing doing nothing, either locked or unlocked (modern electronics). So, after a certain number of days (like 12) there can be a problem when you try to start it -- as with my neighbours. Having said that, my own problems (quite rare) have been due to my wife doing too many short trips in a car and then letting it stand for a few days.
A basic (perhaps even stupid) question - Claude
Surprisingly the best value battery chargers are to be found at Argos, they do an 11amp electronically controlled model for approx £25 whereas that would normally cost at least £35 elsewhere. I also have a small milliamp charger (Draper £10) which I frequently leave connected to my Rangerover battery via the cigarette lighter socket. The voltage has never exceeded 13.8v even when its been connected for a few days so it hsnt had any effect on the electronics. The reason I use it is not because my battery is failing but the following:
- The air suspension system occasionally cycles on and off automatically even when the vehicle is parked up which is a current drain.
- Equipment like heated seats and windscreen put a load on the battery which isnt always recvovered on a short run.
- Alternators dont charge batteries beyond about 80% charge
whilst the draper milliamp charger will get close to 100% over a period of time. So will a three or four stage battery charger with microprocessor control but that costs around £40 (Accumate, Gunson etc) not £10.
Incidently, for a basic 5amp battery charger you wont find anything cheaper than Lidl which have them in stock from this morning at £7.99! There'll be sold out by the end of this week. iw
A basic (perhaps even stupid) question - Cliff Pope
I think RogerL is right. All this trickle-charging stuff that we have heard about for years is completely unnecessary. I would go further and say it doesn't just apply to modern cars and alternators, but to old ones too.
My 1964 Triumph 2000 has an old-fashioned generator. It is used as a second car and so does mainly local trips, totally less than 5,000 miles per annum. The battery was on the car when I bought it 6 years ago. Often it is unused for several days. I have never had to recharge the battery, and it always starts on the button. It is simply a matter of maintaining the car and its equipment in good condition.
A basic (perhaps even stupid) question - billy25
hi ian (all)
this may be a (stupid) answer, but it worked for me!
up until last year i had an old triumph 2.5 p.i, which was used only every other weekend, as a donkey to pull my boat to the shore and back,for a days fishing, nothing more annoying to find the old t-bird (pet name) wouldn't start. however i had a small 150w inverter, and hit on the idea of plugging it into the lighter,and leaving it with a trickle charger connected to the battery,so that it charged itself up while stood.(physician heal thyself- syndrome!)
sorry if i've digressed from the original thread theme,but it justsprang to mind!.

A basic (perhaps even stupid) question - Anglesey Ian
Not a stupid answer at all Billy...

...but interesting nonetheless



Value my car