Assuming you are talking about a lead acid car battery, there are three things to keep in mind when recharging it: voltage, current, and time. Most importantly, you don't want to overcharge the battery, which can shorten its life or even cause it to leak acid.
The ideal voltage for charging a lead acid battery is 2.4 volts per cell. So, for a 12 volt battery with six cells, the ideal voltage would be 14.4 volts. The charging current should be between 10-20% of the capacity of the battery; for instance, a 50 amp hour battery should be charged with 5-10 amps. And finally, the charging time should not exceed 10 hours.
Of course, these are just general guidelines; depending on the make and model of your car battery, you may need to adjust the settings slightly. But following these tips should help you extend the life of your car's batteries and keep them working properly for as long as possible.