The gel batteries can generally be charged up to 30% of their rated capacity (i.e. 90A for 300 Ah). But as they are not wet batteries, they are very sensitive to high voltage, so you should ensure that your smart regulator
is set to Gel mode (no equalisation), and limits the voltage to the maximum voltage advised by the battery
This maximum is dependent of the temperature, so with gel or AGM
it is always better to have a temperature sensor, which generally comes as an option with your battery charger.