# Charging a battery in situ.



## Hintzy (May 31, 2006)

As I don't use my TT that often and my battery is probably original and getting old (but the RAA have checked it and it's still in good condition and is accepting a charge) I'm finding that I need to put the battery on a mains power charger every so often - at present I'm removing the battery from the car to do so but was wondering if it could be left in situ with the cables still connected and charged with the mains power charger without causing any problems?

Any advice from knowledgable others would be much appreciated.


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## Rai (Jun 4, 2005)

Junior Battery Fighter is the answer --> http://www.thebatterywizard.com/prod32.htm

this is what i use to charge and then maintain (float) my battery. my car often sits there for 2 months at a time without driven and my battery never fails to start my car at first turn of the key. with the supplied lead you hook it to the battery and route the plug to the front grille - that way you dont even have to openthe hood to hook your car up to the adapter.


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## Hintzy (May 31, 2006)

Thanks for the reply and advice Rai, 
I don't really want to purchase another charger, I already have a "Smart Charger" and have no issue with lifting the bonnet and don't have a need for the convenience item you have - I just want to derive comfort from the fact that I can hook up my charger with the cables still connected to the terminals with the battery in the car and that no ill effects will occur to anything electrical within the workings of the complex TT system.

I guess with your charger there is no such issue, therefore I gather that what I want to do is OK?


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## Hoggy (May 8, 2002)

Hi Hintzy, As long as your is a "smart charger" shouldn't be a problem. The problems can occur if a high amperage charger is used because the volts can go much higher than normal, & opening TT door puts power to dashpod "DIS" & has been known to cause DIS problems, failure.
H.


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## Rai (Jun 4, 2005)

yeah as mentioned you should make sure your charger is "smart" to allow it to go to float/maintain mode once the battery is fully charged. otherwise my understanding is you can damage the battery. and a weakened battery is something these cars certainly don't take well to with their finicky electronics --> my last battery was faulty and i am sure it caused my airbag module to fault and need replacement.


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## Chip_iTT (Nov 14, 2003)

It is safe to charge a battery in-situ if you follow a few simple precautions:

1/ always connect the charger to the battery before turning it on at the mains (unless it has a proper charge on/off switch - then always ensure it is off before connecting)

2/ always use a good quality smart volt-sensing charger designed for in-situ use - these always check the battery volts and therefore its state of charge before setting the charge current. They can determine the effective charging current (not the current flowing into the system as there are circuits that are permamently powered up in a modern car) by varying the voltage slightly and watching how the current varies - therefore determine the static and dynamic loads.

Most car electronics will cope with voltages up to 25v peak, 15v continuous without failure or overheating. The older non-sensing 'transformer/rectifier' type chargers or even more recent current-sense chargers simply place a high enough voltage across the battery terminals to give a charge current of 1/10 the nominal battery capacity - i.e. about 6A. These types of chargers generally maintain an open-circuit fixed voltage of in excess of 30v and that can be damaging, especially if it is switched on when being connected...


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## KentishTT (Jun 28, 2007)

I just unhook the earth lead if I ever need to charge mine.


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## CHADTT (Jun 20, 2007)

I use a CTEK BATTERY CHARGER, for lead-acid batteries 1.2-120Ah
MULTI XS 3600.

This has an optional ciggy lighter adapter.

Just plug into the lighter socket, power the unit on then using a small button on the charger to set the correct battery type.

This bought back my old battery from a real bad state and keeps it maintained. I only use the car at weekends and it always starts crisply.

The spec is below.

Cost approx Â£60.00.

Voltage AC 220-240 VAC, 50-60 Hz. Output power is
reduced at lower input voltage. A perfect charge will still be achieved.
Current 0.6 A rms
Starting Current < 25 A
Back Current Drain* 1.3 mA
Charging Voltage Nominal: 12 V 14.4 V or 14.7 V.
Ripple** Max 50 mV rms, max 0.13 A.
Charging Current 3.6 A max
Ambient Temperature - 20Â°C till + 50Â°C. Automatic reduction of
power at increased ambient temperature.
Cooling Natural convection.
Charger type Three step fully automatic IUoUp, with
pulse maintenance mode.
Type of batteries All types of lead-acid batteries
(Wet, MF, VRLA, AGM and GEL.).
Battery Capacity 1.2 till 120 Ah
Dimensions 165 x 61 x 38 mm (L x W x H)
Insulation IP 65
Weight 0.5 kg


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## Chip_iTT (Nov 14, 2003)

Thats a reasonable spec charger... one of the most important measures is 'ripple'. Under normal usage a car system isnt expected to see 50Hz ripple on the power line.. the old unsmoothed transformer/rectifier chargers can generate, on an old battery that can't smooth out voltage variations well, 10-12v of ripple - but anything more than 0.5v can be fatal to the tantalum electrolytic capacitors in most modern car electronics (used for decoupling and line smoothing applications). These are very sensitive to power-line ripple and too much can lead to early failure of the insulating gel between the capacitor plates and then to failure of the power management circuits in the associated electronic module.


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