What Battery Do I Need? Battery Size Calculator

Find the right battery size for your setup.

Use this Battery Size Calculator to estimate the battery capacity you need based on your average power draw and required runtime. Enter your loads, adjust for any solar or DC-DC charging, and we’ll show you the recommended battery size along with a selection of matching deep-cycle batteries.

This is a planning tool designed to get you into the right ballpark fast. If you’d like help validating your numbers - especially for WA summers, heavier loads, or longer trips - get in touch and we’ll help confirm the best setup for your needs.

Battery Size Estimator

Estimates are general guidance only. Real-world results vary with temperature, battery health, wiring losses, charge controller limits, and driving patterns.

Recommended Batteries for Your Needs

Based on your inputs, here are battery options that match your use case. Not sure? Give us a call and we'll help confirm the right fit.

How to use this calculator

  1. Select your battery type. AGM/Lead defaults to 50% usable capacity; Lithium defaults to 80%. Choose “Custom” to set your own usable Depth of Discharge (DoD).
  2. Select your system voltage. Most 4WD and caravan setups are 12V. Use 24V if your battery bank is 24V.
  3. Enter your average load (A). This should represent what your setup uses on average, not the peak. If you only know peak draw, reduce it to an average (for example: appliances that cycle on/off).
  4. Enter the runtime required (hours). Example: 48 hours = 2 days off-grid.
  5. Add other constant loads (A) if your “average load” only covers your main appliance and you want to include extra constant draws (lights, pumps, chargers, trackers, etc.).
  6. Optional: Solar contribution (Ah/day). If you know what your solar reliably produces per day, enter it. If you’re unsure, leave it at 0 for a conservative result.
  7. Optional: DC-DC charging. Enter your DC-DC charge current (A) and roughly how many hours per day you expect to be charging (driving).

What you’ll see:

  • Energy needed (Ah) — your estimated consumption over the runtime.
  • Solar + DC-DC offset (Ah) — estimated energy replaced during that period.
  • Required usable capacity (Ah) — what you actually need to draw from the battery.
  • Suggested battery size (Ah) — the nominal battery capacity to target after accounting for usable DoD.
  • Approx energy (Wh) — a helpful cross-check, especially when comparing 12V vs 24V systems.

Tips for better accuracy

  • Use average current, not peak. A fridge might draw 4–6A when running, but the average is lower due to duty cycle.
  • Be realistic about solar. Shade, winter sun, clouds and panel angle can reduce output dramatically. Conservative inputs give safer results.
  • Leave headroom. If you’re right on the edge, choose the next size up so you’re not constantly running the battery flat.
  • Heat changes everything. Fridges and fans work harder in hot weather — plan extra capacity for WA summer trips.

If you want to sanity-check the result, contact Battery Force and we’ll help you dial in the right battery, charging and solar combination.

  • Glad I dropped in here to get a new battery. Helpful, friendly and knowledgable.

    Enjoyed a coffee while the team replaced my battery and had me on my way.

    Great range of other products for 4WD and camping too!

    - Mark Rattigan

  • Thank you SO much to the guys there this morning who very kindly replaced my headlights on the spot.

    The team was friendly and helpful and really went above and beyond.

    - Genevieve Beckett