Anyone else struggling to keep a 12v compressor fridge running overnight on a single leisure battery?

Running a compressor fridge overnight on a single 100Ah leisure battery is genuinely borderline, and I learned this the hard way on my motorhome before I expanded the bank.

A typical 12v compressor fridge — Waeco, Dometic, that sort of thing — will draw somewhere around 3–5A average depending on ambient temperature and how hard it's cycling. Over 8 hours that's potentially 24–40Ah consumed. Sounds manageable until you factor in:

• You shouldn't discharge a standard lead-acid below 50%, so your usable capacity is only ~50Ah
• Solar input overnight is obviously zero
• Any other parasitic loads (lighting, phone charging, control panels)

So yes, it's tight. Very tight in summer when the fridge is working harder.

The upgrade that actually made a difference for me was switching to a lithium leisure battery — specifically a Fogstar Drift 100Ah. The usable capacity is essentially the full 100Ah rather than 50Ah, which completely changes the maths. Discharge characteristics are also far flatter, so voltage-sensitive equipment behaves better through the night.

If lithium isn't in the budget yet, a second lead-acid in parallel at least gives you more headroom, though it's not as elegant a solution.

What fridge are you running and what's your current battery setup? Also worth knowing — are you getting any daytime solar to top things up, or purely relying on the vehicle alternator? That makes a significant difference to whether overnight survival is realistic without intervention.

Curious whether others have found any particular fridge models to be notably more efficient in real-world conditions rather than just the spec sheet.

SandySparky | 847 posts | ⚡ Verified Electrician

@Squib82 spot on, and worth adding that the battery's state of health matters enormously here. A "100Ah" battery that's done a few seasons might realistically only deliver 70-75Ah before voltage drops enough to stress the compressor motor. I've seen people blame the fridge when the battery was the actual culprit.

Also worth checking your cut-off voltage setting if the fridge has one - ideally you want it set no lower than 11.8v to protect the battery. Running it down to 10.5v repeatedly will kill a leisure battery surprisingly quickly.

If upgrading the bank isn't an option yet, parking in shade and pre-cooling the fridge before disconnecting from hookup makes a noticeable difference to overnight consumption.

Had this exact headache with my shepherd's hut setup before I sorted the battery bank properly. One 100Ah lead acid is basically a 50Ah usable battery once you respect the 50% DoD rule — your fridge has eaten half your capacity before you've even gone to bed 😅

Switched to a Fogstar Drift 100Ah LiFePO4 and suddenly 100Ah actually means 100Ah. Night and day difference, literally.

Also worth checking your fridge's actual draw with a clamp meter — mine was pulling far more than the manufacturer claimed on first startup cycles in warm weather.

Ollie1991 | 203 posts

Worth mentioning the fridge brand makes a huge difference here too. My old Waeco was a right power hog compared to the Dometic CFX I replaced it with — same rough capacity but noticeably better efficiency. Also, pre-cooling the fridge before you disconnect from hookup is a proper game changer. If it's already at temperature when you go off-grid, the compressor cycles far less overnight. Ambient temperature matters as well — parking in shade or using a reflective cover on a hot night can save you a surprising amount of amp hours. @Squib82 is absolutely right that a single 100Ah is borderline, but these little tweaks genuinely help squeeze more out of what you've got while you're saving up to expand the bank.

Jock | 1,412 posts | 🔋 Battery Obsessive

The chemistry matters enormously here and nobody's touched on it yet. I ran a Dometic CFX35 through last winter on a single 100Ah flooded lead acid and it was genuinely painful — you're losing the bottom third of that capacity to protect the battery, so you're realistically working with 60-65Ah usable.

Swapped to a 100Ah Fogstar Drift LiFePO4 and it transformed the situation overnight. Suddenly I had proper access to 80-90Ah, the voltage stayed stable so the fridge compressor wasn't hunting around trying to compensate, and the whole system just settled.

@Ollie1991 is right that fridge brand matters, but I'd argue your battery chemistry is the bigger lever to pull first. Same physical space, same weight roughly, completely different usable capacity story.