Running the kids' devices and the fridge: a 12V power budget that works

Last wet season, parked at a free camp south of Rockhampton with the kids' tablets on charge, the fridge running flat out in 31-degree heat and the dog's little clip-on fan going because she was panting on the bed, our battery monitor dropped faster than I expected. It wasn't the fridge that caught me out. It was the sum of everything else running quietly in the background while I wasn't watching.

After two kids, a dog and roughly four years of full-time and school-holiday touring, I've learned that a family 12V power budget isn't really about the big single draws everyone talks about. It's about adding up the small, constant ones that never get their own line item, and being honest about how long your battery actually has to cover them between charges.

Why the fridge isn't the real problem

Everyone fixates on the fridge because it's the biggest single appliance in the van, and fair enough, it is the largest steady draw. A compressor fridge like ours pulls somewhere around 40-50Ah over 24 hours in moderate weather, more like 60-70Ah in a Queensland summer when the compressor is cycling on more than it's off. That's a real number and you need to plan for it.

But the fridge is predictable. It runs whether or not the kids are awake, whether or not we're at a powered site, whether or not anyone's plugged anything in. The problems I've actually had on the road came from the stuff nobody budgets for: two tablets charging overnight, a phone each, a laptop for homeschool work, LED strip lighting left on in the annexe because nobody remembered, and on hot nights, a small 12V fan running for the dog. None of those feels like much individually. Together they can equal or beat the fridge.

If you haven't actually sized your fridge against your battery capacity, our piece on sizing your 12V fridge to your battery walks through that maths properly, and it's worth doing before you add anything else to the ledger.

The daily budget I actually run

Here's roughly what our van draws over a 24-hour period when we're free camping with both kids and the dog, no powered site, no generator:

• Fridge: 50Ah (averaged, moderate weather)
• Lighting (LED, used morning and evening): 4-6Ah
• Water pump: 3-5Ah
• Two tablets + two phones charging overnight: 8-10Ah
• 12V fan for the dog on warm nights: 5-8Ah
• Laptop for an hour or two of homeschool admin (via inverter): 10-15Ah
• Miscellaneous — UHF, USB chargers, the odd torch left on: 3-5Ah

Add that up and you're sitting somewhere between 83 and 109Ah a day, which is a wide range, but that's the honest answer. Devices aren't static loads. Some days the laptop doesn't come out at all; other days it's an hour of marking homeschool worksheets and syncing photos before the signal drops again.

Lithium vs AGM: what it actually changes for a family van

We run a 200Ah lithium bank now, after years on a pair of AGMs. The difference isn't really about weight, although that matters for payload. It's about how much of the rated capacity you can actually use.

With AGM you're generally told not to go below 50% state of charge if you want the batteries to last, which means a 200Ah AGM bank is really only giving you 100Ah of usable capacity before you're doing damage. Lithium (LiFePO4) will comfortably give you 80-90% of rated capacity in daily use, so that same 200Ah lithium bank is giving you 160-180Ah usable. For a family running tablets, a laptop and a dog fan on top of the fridge, that difference is the gap between making it to lunchtime on battery alone and making it through two full days before you need the van running or the solar catching up.

We've written a longer comparison on lithium vs AGM and the real cost per usable amp-hour if you want the full cost-per-amp-hour breakdown rather than my rough version here. Worth saying plainly: I think the AGM-is-cheaper argument mostly falls over once you actually cost it per usable amp-hour over the battery's life, not per amp-hour of nameplate capacity. A lot of forum advice still quotes the sticker number.

Where the kids' devices actually sit in the budget

I did a proper breakdown of this in an earlier piece, because it genuinely surprised me the first time I measured it with a cheap USB power meter. Two tablets and two phones charging overnight from flat-ish to full is only around 8-10Ah combined, which sounds small next to the fridge. The problem is timing, not size. All that charging tends to happen overnight, at exactly the time your solar isn't contributing anything, so it's drawing straight off the battery you need to still have charge in by morning.

If you're deciding between a powered site and a free camp with devices in the mix, the detailed numbers are in powered site or free camp: what your kids' devices actually cost you in amp-hours. Short version: on a 240V powered site the device draw is irrelevant because you're not pulling it from the battery at all. Free camping three or four nights in a row with heavy device use is where it starts to bite, especially under tree cover or on an overcast run down the Victorian coast.

DC-DC charging and solar doing the daily top-up

None of this matters if you can't replace what you used. We run a DC-DC charger off the alternator for driving days and 300W of roof solar for stationary days, and the two cover different gaps.

Driving between camps, the DC-DC charger is doing the heavy lifting, especially in winter or under cloud when solar input drops off. If you're relying on an old-style battery isolator and think your alternator alone is keeping a lithium bank charged properly, it's worth reading DC-DC chargers explained: why your alternator alone won't cut it anymore, because the voltage mismatch between a standard alternator and what lithium wants to see is a genuine problem, not just a nice-to-have upgrade.

On a sunny day parked up, 300W of panel in good sun can put back 90-120Ah, which covers our whole daily budget with a bit to spare. The catch is "good sun." Under the gum trees at a lot of east coast free camps we're lucky to see half that. If you're touring somewhere like the Eyre Highway, the reverse problem exists — plenty of sun but it's a long way between places to actually use the power, which we cover in solar power on the Nullarbor: why the Eyre Highway is a trap for panels.

A monitor is not optional

I used to guess our state of charge off a cheap three-LED voltage display on the wall. It told me almost nothing useful, because voltage under load doesn't tell you what's actually left in a lithium bank the way it roughly does with lead-acid. Since fitting a proper shunt-based battery monitor, I've stopped getting caught out overnight, because I can see exactly how many amp-hours have gone out and how many are left, not just a guess based on a flickering light.

If you're still running on voltage alone, the explanation of why a shunt matters is in battery monitoring: the one gauge that stops you guessing your amp-hours. For a family van with kids' devices adding an unpredictable load every night, I'd call this close to essential, not a nice extra.

What I actually tell other parents

When other families ask me how big a battery bank they need, I tell them to work out their daily number honestly, including the stuff that feels trivial, then build in a buffer of at least 20% for the days the laptop comes out longer than planned or it's a scorcher and the dog fan runs all afternoon. Don't size to the fridge alone and assume the rest is noise.

And if you're weighing up whether a powered site is worth the extra money on a run like the East Coast Run from Melbourne to Cairns, my honest view is that on hot, humid nights with two kids and devices charging, it usually is. The $20-40 a night buys you a full recharge, hot showers at 7am that are actually clean, and one less thing to manage before bed. On cooler nights with good sun the next day, we'll free camp without a second thought. It's not a fixed rule, it's a daily call based on the battery monitor and the weather forecast, which is exactly how it should be.

The Bureau of Meteorology's seven-day forecast and the Australian Government's energy.gov.au solar resource guidance are both worth checking against your own camp diary if you want to get a feel for how your region's sun hours actually track through the year, rather than relying on a panel's rated output alone. For the detail on real-world draw from a laptop, Wi-Fi hotspot and the rest while working on the road, the Clean Energy Regulator's site has useful background on how battery and panel ratings are actually tested, which explains why the sticker numbers rarely match what you see in the van.

We've still got a dog who overheats before any of us do, two kids who think a tablet at 40% is basically dead, and a battery bank that has to cover all of it without me doing mental arithmetic at 11pm. Getting the daily number right the first time has saved me more stress on this lap than any single piece of gear we've bought.