Can I connect my Gyeser brand water heater to solar panel and battery?

Yes, if your solar panel and battery system is able to provide the required power that the water heater needs (voltage, current, etc.). If it cannot do that, the water heater won't work. Whether you will also need an inverter between the solar panel and battery system and the water heater is another issue that can only be determined by checking the specification of the water heater (which will be available from any Gyeser Dealer).

Note: the name of this company is Gyeser, not Geyser.