A good battery charger rule of thumb for charging a lead acid battery, is using a charger with output current (amps) of 10-20% of the battery total stored capacity (Ah).
So, for example if the battery is 12V 100Ah, the charger need to be minimum of 10A and maximum of 20A.  Often splitting the difference at 15% (so a 12V ~15A charger) is a good option. Happy charging!