The Optima YellowTop is a starting and deep cycle battery, making it ideal for our winch-equipped Defender 90.  It’s a bit of a monster – far larger than a standard Tdi starter battery – but it has proved its worth. 
The one we have, the top-of-the-range S 5.5, has a respectable 75 Ah reserve and a cold cranking ampere (CCA) figure of 975 Amps (typical Tdi batteries have a CCA of around 600 Amps), turning the engine over easily, no matter how cold it is.
It has endured numerous full discharges thanks to iffy wiring, but has accepted a recharge each time.
The abuse the battery has had would have killed a standard battery (I’ve lost a few that way), so the fact that it is still working properly is a testament to how good it is.

Verdict: Not cheap, but it’s worth the money.
From: Optima Batteries