The most critical decision when planning an off grid solar system for your camper van, boat, or small cabin is choosing the right battery bank size. Your daily energy use is the primary factor to consider when sizing your battery, another important factor is the chosen charging method.
To put that into perspective if your daily energy use is significantly higher than your battery capacity, unless you have a large fuel cell on standby you will certainly experience an outage. If it’s comparable you may get by literally because the sun is shining (or you may already have a diesel generator or something else on standby).
To make this critical step easy, weโve created a useful Battery Size Calculator. You simply input your daily energy needs and the number of days you can stay powered and we tell you what size battery you would need, lithium or lead acid.
How To Use Our Off Grid Battery Capacity Calculator
To use our battery capacity calculator simply input the following:
- Your daily energy usage (Wh/day).
- Your desired days of autonomy (if going off grid with no charging source).
- Your energy system voltage (12V, 24V or 48V).
- Enter inverter size (VA).
The calculator will then output:
- Recommended Lithium battery size
- Recommended AGM / lead acid battery size
- Safety warnings if DC current exceeds battery limits
Tip: You could determine your energy needs using our Power Usage Calculator and if you get a safety warning please get in touch for further explanation if required.
What Battery Size Do I Need?
How Our Solar Off Grid Battery Calculator Works
We calculate the required battery size using:
B = (T x E x 1.1) / (n)
Where B is battery size, T is the number of days of autonomy, E is the daily energy usage, 1.1 and n is an energy loss factor.
- For lithium batteries n is 0.8, because almost all lithium batteries have a usable capacity of 80%
- For lead acid batteries n is 0.5 because almost all lead acid batteries have a usable capacity of 50%
- The 1.1 factor is to account for energy loss in the entire system (assuming it runs at 90% efficiency) in cables and the inverter (when converting DC to AC).
Why Battery Size Matters
Your battery bank stores the electricity generated by a DC DC charger, a generator or solar panels, having a roperly designed system ensures you can power all your appliances safely, reliably and cost effectively.
Also some times you want to intentionally oversize a charging source compared to your battery size. Here are some examples:
- There’s space for a cheaper charging source
- Unreliable weather conditions
- You want extra control on how and when to charge
As long as your battery size can comfortably cover your daily energy needs you are better off oversizing your charging sources than a battery because:
- Charging sources like solar panels are cheap
- Your battery life will be extended (less discharging)
Lithium vs AGM Batteries: Whatโs Right for You?
| Feature | LiFePOโ (Lithium) | AGM (Lead-Acid) |
|---|---|---|
| Usable capacity | 90โ95% | 50% |
| Lifespan | 2000โ5000 cycles | 500โ1000 cycles |
| Weight | Lighter | Heavier |
| Cost | Higher upfront | Lower upfront |
| Maintenance | Minimal | Requires monitoring |
Tip: Lithium batteries are ideal for camper vans, boats, and off-grid cabins where space and weight matter. AGM batteries are still reliable for budget setups or backup systems. You could find more detailed information about this topic on our complete guide on Leisure batteries for Caravans, Campervans and Motorhomes
Now that you know what battery size you need feel free to explore the wide range of leisure lithium batteries we offer or our home lithium batteries.
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