Marine Battery for Defender?

[Ranga]

I'm looking to replace my cranking battery and auxiliary battery. My current cranker is a 4yo Caterpillar battery, which is getting a bit tired. The auxiliary is a Century marine battery of the same age, and is buggered. Any reason why I shouldn't/should go another marine battery?

Any other battery suggestions?

[Toxic_Avenger]

I have 2x Optima 'Blue tops' in the group 34 size. Works for me. They are a hybrid style battery - a mix of deep cycle and cranking
The blue tops are the same specs as the yellow top, just with additional threaded post terminals for additional accessories (above and beyond the SAE posts).

[DiscoClax]

I have the same in the D1 (2x blue tops). Seems to work a treat. The cranking battery is about a decade old and still working like a new one. The aux is only a couple of years old... so far.

[Ranga]

I decided to just replace my cranker with a Supercharge MF95D31R, and will drop a deep cycle AGM in as the auxiliary.

[Slunnie]

Been using Blue Top for about the last 15 years - they're a great battery.

[DiscoMick]

I decided to just replace my cranker with a Supercharge MF95D31R, and will drop a deep cycle AGM in as the auxiliary.Good move. Starting and auxiliary batteries are different.
Starters give a big charge to start and do very little else. They have thin walls. They recharge fast.
Auxiliary batteries have thicker walls and are designed to give a slow discharge. They recharge more slowly.
Using them for the wrong purpose damages them.