Hi Frank
In my V2C I just press the taller 10.5AH battery in the front holder.
The 2 retention clips stay spread out and stay on the side.
But the battery cannot go anywhere even with the restrains not being
on top (as they are supposed to be with the 7AH battery)
My 2 main batteries are still the 7AH.
But this winter I am going to fabricate a new taller bracket to also
accommodate the taller 10.5AH batteries in the main compartment.
Due to CofG, I am not using the tail battery
In the past I have been running the 7+7+10.5AH with a old Terra
transponder, an old GPSMAP195, an old LNAV (all power hogs) with no
problem.
Currently I have the TT21, IPAQ310, LNAV+Etrex.
This setup uses even less power.
I am waiting for the PowerFlarm, but that is a minimal power add-on.

Having separate power circuits for your (modern) transponder is just
adding unnecessary wiring complexity to your system.
You can have all 3 batteries switched in parallel and just have 1
power feed.
The 2 7AH main batteries are switched together in any way (at least on
my ship)
It is better to invest your effort in a good fat power bus running
from your batteries to your power distribution panel.
In my ship I replaced the original power bus (ground of all batteries
running through 1 wire of a 25 wire printer cable) by a fat 12 AGW
Tefzel cable.
Since then I don't have power supply problems anymore, like
unexplainable premature voltage drop.
Of course you have to charge the batteries separately.
Hans Van Weersch (3U)