My 1914 has a motorcycle battery wedged between the gas tank and the left side of the body. As far as I can tell, the previous owner unbolted the tank to get the battery in, not too convenient. I don't seem to be armstrong enough to start the car cold on Magneto, and so I think a new battery is in order.
On my other antique cars, I've been using Optima batteries, and I'm completely sold on the advantages of AGM batteries, due to their light weight and spill-proof properties. They can lay on their side also.
I know the needs of a starting ignition battery for a T is quite different than other cars. What are other people using? Battery technology is advancing very quickly in recent years.
Here's what I did on my 1915:
I use a 12v electric fence battery that I got at Tractor Supply, put some wood blocks and hooks in place and use a small bungee cord to secure it in position. Works great to start. It is a sealed battery that I can hold in one hand, and I can take it out easily to recharge with it's small charger in a motel room, etc. Been using the same battery for about 4-5 years.
I chose a 12-volt, Optima red-top for my '15 Touring and it was installed beneath the floorboards of the back seat, in a standard Model T battery rack, in the standard battery location for later-vintage Model T Fords. -The red-top Optima is made for short bursts of cranking power, but in retrospect, the blue-top boat battery, which is made to stand up to frequently repeated cycles of deep, lengthy discharge, might have been a better choice.
Access to the battery is by lifting out the back seat floorboards and that only requires unscrewing two pieces of wooden trim. -It is convenient to just store the two trim pieces in my garage because I need to access the battery frequently for recharging; the floorboards now being held down nicely enough by the standard, straw, rear-seat Model T floor mat which is heavy enough to keep the boards from rattling. -I don't know if I'd be comfortable wedging a battery up against the fuel tank as you have.
You can let your car charge your battery. See my link above.
This is where I put my battery.
The bottom of the box extends to under the tire mount so I didn't drill any new holes.
The cables go thru a hole in the back of the battery and between the body and skirt.
I now use a rope to hold up my pants!