Some machines systematically charge the SLA battery, for example some home alarm or backup systems. Meaning, you do not have to take the battery out and charge it on a battery tender.
If you do need to charge your SLA battery with a battery tender, selecting the correct battery charger will impact the performance and service life of a sealed lead acid (SLA) battery. As a general rule of thumb when selecting a charger for an SLA battery is to use one that is no more than 20% of the capacity rating of the battery (at a 20hr. rate).
Example; to charge a 12 volt / 7.5Ah battery select a charger with a maximum charge output of 1.5 Amps (7.5 x 0.20 = 1.5).
To charge an automotive battery, refer to your owner´s manual and your battery charger manual for instructions. Read and follow all safety and handling instructions that came with your charger and battery. Battery chargers will charge a battery based on its condition and at a rate appropriate for its state of charge. Charging voltages run from 13.8 volts to a maximum of 15.5 volts for most applications. Finally, remember that batteries contain sulfuric acid that can cause severe burns, and hydrogen-oxygen gases that can be explosive. Charge in a well-ventilated area. Be sure to follow all safety and handling.