If you have a car charger for your phone, it's likely that you can also use it to charge a SLA battery. But there are a few things to keep in mind before doing so.
First, make sure that the car charger is rated for the voltage of the SLA battery. Most car chargers are rated for 12V, but some may be higher or lower. If the voltage is too high, it could damage the battery. If it's too low, it won't charge as efficiently.
Second, check the amperage rating of the charger. The amperage will determine how fast the battery charges. A higher amperage means a faster charge, but make sure not to exceed the maximum amps that the battery can handle.
Finally, consider using a voltmeter to monitor the charging process and make sure that everything is working as it should be. With these precautions in mind, go ahead and give it a try!