Anyone else struggled to keep a small log cabin warm without going overboard on battery capacity?

Been through this exact headache with my cabin setup. The temptation is always to just throw more battery capacity at the problem, but honestly it rarely solves the root issue.

What made the biggest difference for me was tackling insulation properly first — specifically the floor and any gaps around window frames. Lost an embarrassing amount of heat there before I bothered to check. Once that was sorted, my heating demand dropped noticeably and the batteries I already had (a modest 200Ah lithium bank from Fogstar) stopped getting hammered overnight.

For actual heat I use a small wood burner as the primary source and a 12V diesel heater as backup when I'm not there to tend a fire. The diesel heater is surprisingly efficient on DC draw compared to anything resistive. Running an immersion or electric panel heater off batteries in a poorly insulated space is basically just burning money.

A Victron BMV keeps me honest about what's actually going on with consumption — worth every penny for the visibility alone.

A few questions worth asking yourself before buying more batteries:

• How thick is your floor insulation?
• Are you relying on resistive electric heat?
• What's your overnight temperature drop typically?

Curious whether others have found the cabin size makes a big difference too — mine is fairly compact which definitely helps retain heat. Does anyone have experience with slightly larger builds, say 20x12ft or bigger? Wondering at what point you genuinely do need to upscale the battery bank rather than just optimise everything else first.

@JulieAllen what was the root issue in your end? You've cut off mid-sentence so curious what the actual fix was.

For my shepherd's hut I went down a similar rabbit hole — kept adding capacity thinking that was the answer. Turned out the real problem was thermal envelope. Once I sorted proper insulation (sheep wool batts, fittingly) and draught-proofed the door properly, my heating load dropped significantly and my existing 200Ah Fogstar lithium bank suddenly felt more than adequate.

Are you running any active heating, or purely passive? And what's your heat source — diesel, propane, or purely electric? That changes the calculation massively for overnight battery draw.

@JulieAllen did you ever finish that sentence? 😄

From my garden office experience — insulation was always the elephant in the room. I was throwing kilowatt-hours at a basically cold box before I sorted the floor insulation properly. Massive difference.

For a log cabin specifically, the log joints are usually where you're haemorrhaging heat. Worth checking with a thermal camera before assuming your battery bank is undersized. Victron kit will happily show you exactly how much you're drawing overnight and it's often a shock.

My rule of thumb: if you're running a heating element more than 3-4 hours to maintain temperature on a mild night, the building envelope needs attention before the battery bank does.