TECHNICAL EXCELLENCE

Re: Please Educate Me About Car Batteries/Charging
Posted by JCB on Thursday, 23 April 1998, at 8:38 p.m.

Martin

In a prior life I was an electrical engineer although I did not particularly specialize in batteries. At the rebellion I was the one who asked the question regarding the removal of the battery for charging because I found that advice unusual. The reps answer had two parts which matched my thoughts pretty well. The first point is the sensitive electronics on board. To charge a battery a voltage higher than that of the battery must be applied. Your car's alternator will put out a voltage of 13-15 v to keep the battery charged. The higher the voltage applied, the more current through the battery (Ohms law) and the faster the charge. Some fast chargers are capable of rather high voltages, to say nothing of a charger capable of handling 28v batteries. Porsche recommends removing the battery because that is the only way they can protect the electronics from somebody using the wrong charger or setting. The second reason is that with a fast rate of charge the electrolyte will heat and or boil. If you manage to push enough of that acid around the interior of the car it will probably ruin your whole afternoon:).

The Porsche battery maintainer or any quality trickle charge can safely be used to maintain a charge on the battery and I use one when I don't run the car for long periods of time. In addition to the computers draining the battery, the life is shortened if it is allowed to deeply discharge and just sit. You should not attempt to jump start or fast charge the battery through the lighter jack, at best you'll blow a fuse.

I see no reason why the car cannot be safely jump started from a properly running car if the cables are hooked up properly.

As a word of caution, fooling with 12v lead/acid batteries is dangerous and if you are not comfortable doing it - Don't. When working with batteries you need to have penty of ventilation (the gases are explosive), remove jewelry (ever see an arc welder - low voltage, high current), wear protective clothing and eye wear (remember the acid) and use caution.

Regular preventative maintenance: - Keep battery charged but do not over charge - automatic type trickle chargers work best. - Check electrolyte and add distilled water to recommended level -Avoid deep discharges, like I left my lights on on purpose? - Turning off unnecessary accessories and lights before starting the car will decrease the load on the battery during cranking. - Never remove a battery from a running car - lots of damage to the electronics

Hope that helps

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