Obviously (it appears?) you did something wrong. So correct connection error. Also when you say batteries replaced? What with? Did you check voltages?
You may have installed a discharged battery. If these were new they should both be above 12.7V on delivery. Or return. And both should be fully charged, or at least connected together in parallel for 24 hours before installing and charging normally.
And check all connections, even the ones plugged into the power module, or bus cables etc.
Batteries are 12volt- 55AH AGM fully charged. Checked cables to batteries are correct and tight. When I turn it on there's nothing showing on the display screen. It's blank. Is there a reset for the controller or an inline fuse somewhere that I may have missed?
Did you wire the batteries in series for 24v? If you wire them in parallel then the chair will not turn on because it needs 18 volts or more to operate.
I would start over. Remove the batteries check voltages then connect in parallel for 24hrs then separate the batteries from parallel then take your time an reinstall them in the chair in series double checking each connection is correct as you go.
Is there a reset for the controller or an inline fuse somewhere that I may have missed?
Not to my knowledge ..No..
If you have a multimeter you can probe the charging socket ...if the reading is around 13v you have wired the batteries in parallel.... if the reading is zero then you have a wiring / connection fault.
An expert is a person who has made all the mistakes that can be made in a very narrow field. Niels Bohr
In many chairs with two batteries there are two Anderson connectors - one connected to the "outer" 24V + and - terminals and feeds power to the chair, the other goes from the "inner" + and - terminals that goes to a fuse or circuit breaker. If you reversed where these are connected the chair will not go!
I want to thank everyone for the help with my problem. It turned out to be a bad fuse inline between the Anderson connector and the battery terminal. I replaced it with a 125 Amp Mega fuse an exact replacement part. Thanks again.