yo! Honestly, for a Defender 110 build like yours, you gotta think about the 'Depth of Discharge' vs 'Cold Cranking Amps'. Basically, your winch needs high burst power, but that fridge needs slow, steady drain. If you're staying stationary for 3 days, you definitely need a setup that wont leave you stranded.

Since you want to stick to a budget but still get PRO performance, here is what I recommend:

1. **The Heavy Hitter:** Check out the NorthStar NSB-AGM31 Blue Battery. It is basically the secret weapon for Landy owners. It's built like a tank to handle those corrugated roads and has a massive reserve capacity for the fridge cycles. Usually runs around $450-$500, so it fits your budget perfectly!

2. **The High-Value Alt:** If you want to save a bit for other gear, look at the VMAX SLR125 AGM Deep Cycle 12V 125Ah Battery. It is a beast for deep cycling (perfect for the fridge/comms) but is still rugged enough for the Pyrenees heat.

I mean, Lithium is cool and all, but in an engine bay with high vibration? AGM is still king for reliability in my book. Good luck with the build, the Pyrenees are gonna be AMAZING! 👍

Honestly, I feel u on the anxiety of a dead battery in the middle of nowhere. I've been running Defenders for over 15 years, and for a rig that's gonna see corrugated roads and Pyrenees heat, I'd personally stay away from Lithium in the engine bay for now. It's just too risky with the heat soak.

In my experience, you're basically looking at a battle between Odyssey and Optima. I've tried both, and for a heavy-duty expedition build, I would suggest going with the Odyssey Extreme Series Group 31 Battery 31-PC2150. It's a total beast. I've had one in my 110 for five years and it handles the winch loads and my fridge like it's nothing. The vibration resistance is top-tier because the plates are packed so tight.

But yeah, if you want a dual setup, maybe look at the Optima BlueTop D31M Dual Purpose Battery as your auxiliary. It's great for deep cycling but can still crank if ur primary dies. Seriously though, make sure to grab a quality DC-DC charger like the Redarc BCDC1225D Dual Input 25A In-vehicle DC Battery Charger to manage the flow. Without it, your alternator might struggle to fully top off those AGMs, especially when you're stationary for three days. It's a bit of an investment, but way cheaper than a recovery mission!! basically, stick with high-end AGM for the reliability and you'll be golden. gl with the build! 👍

Any updates on this?

Sooo I went through this last year prepping my rig for a similar trip, and honestly, the anxiety is real. I ended up going with a dual setup because I just didn't trust a single unit to handle the winching plus the fridge draw for 3 days straight... it's a lot to ask! I was pretty worried about the engine bay heat in the Pyrenees too, so I stayed away from Lithium for the starter.

Technically, if you want something that's basically bomb-proof for vibration, I've had good luck with these:

1. Northstar NSB-AGM31 Ultra High Performance AGM Battery - This thing is a beast with 1150 CCA. It's built like a tank and handled corrugated tracks way better than my old stock unit.
2. Fullriver DC115-12 Sealed Deep Cycle AGM Battery - This is what I used for my house battery. It's a true deep cycle, so it handles those 50L fridge cycles without complaining.
3. REDRARC BCDC1225D Dual Input 25A In-vehicle DC-DC Battery Charger - Make sure to use one of these to keep everything balanced, especially if you're mixing battery types.

Just be careful with the weight tho, those Group 31s are heavy af! But yeah, the peace of mind is worth the extra pounds imo. gl!

Seconding the recommendation above about the dual setup. Honestly, I've seen too many people fry their electronics trying to go Lithium in a hot Defender engine bay, so be careful.

I mean, if you want something bulletproof, maybe look at NorthStar NSB-AGM31 High Output Battery. It's basically a tank and holds up way better against those corrugated roads than an Optima. Also, the Fullriver DC115-12 Deep Cycle AGM is a solid alternative if you're prioritizing that 3-day fridge draw over winching power. Just make sure to double-check your mounting bracket, those things are heavy lol. Good luck!