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Message: <blockquote data-quote="jarance" data-source="post: 97486" data-attributes="member: 21">Actually, it depends on the voltage output of the charger. Even though it states 12V Dc, chances is that the voltage output could be at least 1.2 X 12 VDC. Some of the charger comes with "boost" charge and "trickel" charge mode. In the boost charge mode, the voltage is higher in order to quickly charge the battery. Normally you use this mode when the battery is nearly flat and need a quick charge. However, this mode is not recommend as it will not fully charged the battery. The normal output voltage can sometime be as high as 1.4 X 12 V DC = 16.8 VDC.. Because of the high voltage, it might not be recommend for some electronic ae they are rated to +/- 20 % tolerance.Note: If you plan to stored your battery after charging, do not use boost charge as the charge does not retained too well when the battery is charged in this mode.In the trickle charge, the output voltage of the charger is lower. Normally about 1.2 X 12 VDC = 14.4 V DC. This mode is recommend in most case as the battery tends to retain it charge better. However, the duration is longer due to the slow charge.Note: There are some chargers that have auto charge mode. i.e. it can start charging the battery on boost charge first and switch to trickle charge when the voltage and current draw is less from the battery.Most of the battery used by cars are Lead Acid type. There are some manufacturer who produce maintenace free battery but they are relative slightly more expensive than the conventional type.My advise is to disconnect one of the terminal from the car battery when you intend the battery with a portable charger. Make that the area is well ventilated as the battery gives off acid fume during charging.</blockquote>

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