Solar roof ventilation fan - Add lithium battery?

[darrenjc]

Hi,

I have a basic roof ventilation fan with a 12v solar panel built in.  (Bunnings Ezylite 200mm Solar Roof Vent Fan)

It works great but I don't want it to stop when the sun goes down, so I was thinking of adding a 12v battery in parallel to keep the voltage up and spin the fan...

However, I know it's not that simple.

Issues -

Overcharge - I'm sure the battery would try to overcharge and id need way to limit current when it's charged.
Current - I can measure the current demands during the day to see how much it draws, then spec the battery to last overnight.


Do I need a charge controller?
Can I just build a simple charging circuit?
Will the solar panel have enough power to run the fan as the priority, but also trickle charge the battery durign the day?

12v solar
12v motor
Current - Probably only 300mA?


Thanks in advance