07/04/2026
Caravan Battery Maths – Made Simple
Unsure about Volts, Watts, Amps, Amp Hours, Lithium, AGM and what it all means? This is a long post—but worth the read.
Over Easter I had several enquiries asking: “Why is my caravan battery flat? It’s fairly new.”
In both cases, they had been sold the wrong setup.
This post will give you a basic understanding so you can make sure you’re getting what you actually need.
AGM vs Lithium Batteries
If you’re only running lights, a radio, or a TV—an AGM battery is fine.
If you’re running high-power gear like an inverter for 240V appliances (toaster, coffee machine, hair dryer, etc.), you need Lithium—and here’s why:
Think of your battery like a bucket of water:
Each litre = 1 Amp Hour (Ah)
AGM (100Ah battery):
100L bucket, but only 50L usable (using more causes damage)
Max discharge: ~50A
Max charge: 20–30A
Lithium (100Ah battery):
100L bucket, with ~80L usable
Max discharge: ~100A
Max charge: 50–100A
👉 Lithium delivers more power, faster—and charges quicker. That’s why it suits high-demand setups.
Inverters – Power Hungry Monsters
If you’re running appliances like:
Toasters
Coffee machines
Hair dryers
You’ll need an inverter—but how big?
👉 Rule of thumb: Go slightly bigger than you need.
Check your appliance rating:
Example: Toaster = 1000W
Now do the rough maths:
Watts ÷ 10 = Amps from battery
1000W ÷ 10 = 100A from your battery.
That’s what your battery must deliver.
If it runs for 6 minutes (1/10 of an hour):
That’s 10Ah used (10L from your bucket)
Now you can see:
👉 An AGM battery can’t handle this load (it will try… until you damage it).
A better setup:
200Ah Lithium battery
1500W inverter
This gives you a buffer—but remember:
👉 You can only run one appliance at a time.
Recharging Your Batteries
DC-DC Charger (from your car):
40A charger = twice as fast as a 20A
Example: 200Ah battery at 50% charge 100Ah needed
20A charger → ~5 hours driving at best
40A charger → ~2.5 hours at best
Solar Panels
As a rough guide:
250W panel ≈ 10A per hour (in ideal conditions)
So in one good HOUR of sun:
You’ll put back 10Ah (your 6 minutes of toast!)
But:
Winter sun is lower,Fixed panels on your van can’t be angled properly
👉 Solution:
Install plenty of solar on your van plus, add a portable blanket panel you can aim at the sun
Buy Quality Gear
Cheap gear often:Underperforms
And ratings can be questionable
👉 If it’s half the price of everything else—there’s usually a reason.
Also:
Do your own research
If a salesperson is just reading the box… you can do that yourself
You should be getting proper advice, not guesswork.
Real Example (Easter Sunday, Phone call for help)
Customer setup:
125Ah AGM battery
3000W inverter
Running a 1500W coffee machine + toaster
Let’s do the maths:
1500W ÷ 10 = 150A draw
Battery capability:
~60A max
👉 Result: Destroyed battery.
And yes—the setup had been inspected by the shop for what was needed.
Final Takeaway
Learn the basic maths and think of your battery as a bucket of water, you put Amp Hours in and out
Once you understand the concept you will be better equipped to ask the right questions.
David
DKZ Mobile
📞 0403 924 911
