Thank you for your post, lots of good information here.
I have a 2024 spyder RT too, as for my battery, I still have the Haijli battery, and so far its starting the spyder, but thinking of replacing it if problems come up. I had to replace my 2018 RT battery when it just died unexpectedly on a ride.
AS for the reverse problem, I had the same thing on my 2018 RT, sometimes would not go into reverse, it turned out to be in the reverse control button on the handle bar, I fixed it before taking it to the dealer, I have read on the forum where other people had the same problem and waited days to months for the dealer to replace the switch.
But that's not the problem you have, but close.
As for the low reach handle bar, I noticed I had to reach further on my 2024 compared to my 2018, and both have a back rest.
I added 1.5" to the 2024 back rest to bring it up a little higher, so it's pressing higher on my back.
I also added 1" long round blocks under the handle bar holder to raise it up and back, its better, and the extra benefit is I can see what's behind me in my mirrors instead of seeing my hands. I see this is a option from the third party resellers, and may try 2" risers to see if that helps, I know it will help to see what's behind me.