Challenger Long Range Fuel Tank

Check with ARB. In some cases they replace existing tanks with bigger. They handle the Long Ranger range, I don't know if there are other brands available.
Can't help with the battery, maybe ask them also.Carpe Diem

I had a long range tank fitted to my 99 Challenger. They replaced the old tank which fits on the passenger side. It's 115litres & I got it from Opposite Lock (although I believe they have stopped making them now you might find they still have one in store). I picked up the last one they had in WA & it was fitted for $800- all up. I don't thik the low fuel light works anymore but the guage is all you really need anyway.
I'd be surprised if you could get a 2nd battery under the bonnet (although there might be room if you don't have an air compressor mounted under there.Here's Mud in your Tyre

Hi Mike, I had ARB (brissie) fit a second battery in my 01 Challenger. It ended up nexxt to the other one in the top right corner. The charcoal canister was relocated to the top left.

Cheers, Juma