Anyone else struggling to keep a 12V compressor fridge running overnight on a 100Ah lithium?

I've got a BougeRV 30L compressor fridge in my Transit conversion and it's absolutely hammering my battery. Running a single 100Ah LiFePO4 (Fogstar Drift), and by about 5–6am the BMS is cutting out around 20% SOC. The fridge is drawing roughly 4–5A when the compressor kicks in, maybe averaging 2A over an hour once it's settled at temp — ambient in the van was probably 18°C overnight so not roasting.

Done the maths and 100Ah should be enough in theory, but I'm wondering if my fridge is working harder than it should be. It's set to 4°C, lid seal seems fine, and I'm not opening it constantly. I did notice the compressor seems to cycle on more frequently than I'd expect — maybe every 8–10 minutes for a couple of minutes at a time.

Has anyone dialled in a similar setup? Curious whether it's worth adding a second 100Ah battery or if I'm missing something daft like poor ventilation around the fridge. It's currently tucked into a cabinet with about 30mm clearance on each side — wondering if that's the culprit.

@CamperBaz the maths here is fairly unforgiving — a 30L compressor typically pulls 3–5A average depending on ambient temperature and setpoint, so over 8 hours you're looking at 24–40Ah minimum. Factor in that LiFePO4 shouldn't really be drained below 20% usable (so you've effectively got ~80Ah working capacity), and you're borderline even on a cool night.

In my shepherd's hut setup I found thermal mass made a significant difference — pre-cooling the fridge aggressively before sunset and keeping it well-stocked (water bottles act as thermal ballast) drops compressor duty cycle noticeably.

Worth checking actual draw with a Victron SmartShunt rather than guessing — the BougeRV units can spike considerably higher during startup. A single 100Ah is genuinely undersized for full overnight fridge use without some solar top-up during the day.

100Ah sounds heroic until your fridge doesn't get the memo that it's supposed to share.

@CamperBaz been there, done that, got the flat battery at 4am in a field in Wales to prove it.

Honest answer: 100Ah is just undersized for overnight fridge duty unless ambient is cold and your fridge isn't working hard. Rule of thumb I use is never plan to draw below 20% SoC, so you're realistically working with 80Ah usable — and your fridge is eating a good chunk of that before midnight.

Few options:

• Add a second 100Ah (Fogstar Drift again, dead easy to parallel)
• Insulate around the fridge to reduce duty cycle
• Pre-cool contents before switching to battery

I run 200Ah in my cabin setup and the fridge still surprises me in summer. More capacity is basically never the wrong answer with LiFePO4, it's not like lead where you're crying over every kg.

Had this exact issue with my setup last summer. The thing people miss is usable capacity — your Fogstar Drift is great but you're realistically working with maybe 80Ah before the BMS gets twitchy, and that's before voltage sag under load makes it worse.

What sorted it for me was adding a second 100Ah in parallel. Doubled the capacity, halved the stress on each cell, and the BMS stops throwing a wobbler at 3am.

If a second battery isn't an option, look at your fridge placement and insulation first — a well-insulated fridge in a cooler ambient will cut compressor run time significantly. Pre-cooling contents before you set off helps too.

Also worth checking your actual draw with a Victron BMV-712 if you haven't already — you might be surprised what else is nibbling away overnight.

@OllieThompson73 is absolutely right to flag usable capacity, but the ambient temperature piece is equally critical and often overlooked. A compressor fridge in warm weather can easily pull 3–5A average depending on how hard it's cycling. Over 8–10 hours that's potentially 30–50Ah minimum — and that's before you account for anything else drawing from the bank.

On my motorhome I run 200Ah of Fogstar Drift paired with a Victron SmartShunt, and the shunt data genuinely transformed how I understood my consumption patterns. Without real monitoring you're essentially guessing.

My practical suggestion: log actual draw over 24 hours before assuming the battery is undersized. The fridge door seal, internal temperature setpoint, and ambient all vary the figures dramatically. You may find optimising those before spending money on more cells.

Great points from @OllieThompson73 and @RustyRoamer already. One thing worth adding, @CamperBaz — have a look at your fridge's thermostat setting and whether it's sitting in direct airflow. A poorly ventilated compressor fridge works significantly harder than it needs to, which absolutely murders overnight draw. Also worth checking what temperature you've actually set it to — people often run them colder than necessary. For drinks and general food, 7°C is perfectly fine rather than pushing it down to 2°C. That alone can make a noticeable difference to duty cycle. If you've got a decent multimeter, log the actual current draw over a few minutes and work backwards — you might find the real consumption is higher than the spec sheet suggests, especially if the fridge is a bit warm from being loaded with non-chilled food beforehand.

Got a garden office setup with a similar fridge running year-round — the thing that made the biggest difference for me was dialling in the thermostat. Most compressor fridges default to way colder than needed, mine was sat at 2°C when 6–7°C is fine for most stuff. Cut duty cycle noticeably.

Also worth checking your cable gauge and connection quality — voltage drop under load means the fridge works harder than it should. Swap to proper Anderson connectors if you haven't already.

100Ah is honestly tight for overnight though. If you can't add capacity, a small pre-cool session before bed helps.

@CamperBaz one angle nobody's touched on yet — duty cycle creep at night. Counter-intuitively, fridges often work harder after midnight in a van because the thermal mass of the cab drops significantly, and if your fridge is near an exterior wall or floor, it's fighting conduction losses rather than just ambient air temp.

Worth logging actual runtime percentage using a Victron BMV or similar shunt — if you're seeing 60%+ duty cycle through the small hours, insulating around the fridge unit (not blocking ventilation) makes a measurable difference. I did exactly this on my static caravan backup setup and knocked roughly 15–20% off overnight draw.

Really resonates with my cabin setup. I ran a similar-sized compressor fridge off a single 100Ah for one miserable winter before I accepted the maths just don't work once ambient drops and the fridge starts chasing temperature.

What finally sorted it wasn't a bigger battery — it was insulation around the fridge itself. A simple reflectix wrap and making sure hot air could actually escape behind the unit cut my overnight draw noticeably. The compressor wasn't running nearly as hard.

@FormerTeacher61 is spot on about night duty cycles too — often the overlooked culprit. Worth logging actual consumption with a Victron BMV before assuming the battery's the problem.