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Discussion Starter · #1 ·
In the old car (a Rover), due to short journeys and light use, AA homestart recommended running the car on the drive once a week, and using a maintenance charger to avoid the battery going flat.

Despite the fact that the manual said to always remove the battery before charging. The Hyundai manual says the same.

Is this just the manufacturer covering themselves?

Is it really an issue to attach a maintenance charger with clips to the battery while its in the car, this seems to be what I see people doing, but maybe modern cars have more electronics that could be affected?
 

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2008 Accent 3 dr 5 sp manual; 2010 Genesis Coupe 2LT track 6 sp manual
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I have never removed a battery just to charge it. It is a CYA situation by the manufactures and pointing to a possible charger defect. What about when you are driving and the battery is always being charged?
 

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You can charge a battery with it hooked up to the car. Just make sure the negative side of the charger is connected away from the battery terminal. The frame where the negative terminal connects to, the alternator housing, any other grounding point, etc. I'm a big fan of the battery tender brand for maintenance charging.
 

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I think that the concern is that some older (or really cheap) battery chargers may source some high voltage (over 15V, but still too low to cause a shock) pulses that could damage the electronics. Even this is unlikely to happen as long as the battery is in good shape (the battery would adsorb/filter the pulses out).


The battery tender type chargers are no risk at all for this, and the newer better quality chargers should be safe too. I've never disconnected batteries to charge them using reasonably decent chargers, and haven't had any problems. Just don't use that 1970s high speed boost charger with the battery connected.
 

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The reason the manual recommends disconnecting the battery during charging is because some cheap chargers have poorly regulated outputs. The electrical noise produced by these cheap chargers can cause problems with the cars electronics. Personally, I rarely disconnect a battery when I put it on charge and I've never had a problem, but I do have a good quality charger.

BTW, some manufacturers tell you not to disconnect the battery while charging it, and to connect the negative charger lead to the engine block rather than the battery negative post. The reason being the battery sensor on the negative battery terminal needs to measure how much current has passed into the battery during the recharge so the battery control module can calculate the battery's state of charge. This doesn't apply to Hyundai though because they don't have battery control modules.
 

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Some cheap battery chargers have high 'ripple' where the voltage is not steady. I would recommend using a high-quality charger such as a CTEK charger which has next to no ripple at all. And you can leave it connected when you go on holiday with no ill-effects!
 

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I remember when my dad had a Morris Minor in London. It was only used weekends and because it had a dynamo he was always using the starting handle and a battery charger. I don't believe with our modern cars you would need to charge the battery at all. You can leave the car at the airport for two weeks and it bursts into life. Maybe wise just to stop fretting and let the wonderful modern alternator top your battery up in a very short time. I haven't possessed or used a battery charger for the last thirty years and been retired for nine. I do about 3k miles a year and the thing just works brilliantly.
 
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... I don't believe with our modern cars you would need to charge the battery at all. You can leave the car at the airport for two weeks and it bursts into life. ...

A couple of weeks, no problem. A couple of months, problem.

"Modern" cars actually have more of a drain on the battery while they are sitting than much older cars did. The old cars might have a little drain for the clock, but that was about it. Newer cars have a drain for the alarm system, the remote unlock receiver, and in some cases a cellular transceiver (Hyundai remote start), and the smart key system.
 

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I have had a couple of modern cars where the battery would go flat in a week if not disconnected and the engine not run to charge it. In fact I got a good deal from a guy who could never start his car and didn't understand this. I took a battery charger to his place, charged the battery and away I went. As the post above, this is caused by the constant drain caused by immobilisers and suchlike.
 

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I park my Gen Coupe over the winter. If I don't disconnect the battery in a month it will be run down too much to start.

There are a few reset procedures; the power windows, AC defrost logic and sunroof that I need to do when connecting it back up and the radio stations. The reset procedures should be in the owners manual if there are any.
 
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