RV & Campervan 12V Battery Bank Usable Runtime & Inverter Sizer
Running out of power mid-trip is a common boondocking mistake because usable capacity is much lower than the printed amp-hour rating once depth of discharge is factored in. This calculator converts your battery type and daily appliance load into real usable watt-hours and estimated days off-grid.
Your battery bank provides about 1.8 days off-grid at 600 Wh/day usage.
| Measure | Value |
|---|---|
| Battery type | lifepo4 |
| Capacity | 100 Ah @ 12V |
| Depth of discharge | 90% |
| Usable Wh | 1,080 Wh |
| Daily appliance draw | 600 Wh/day |
| Days off-grid | 1.80 |
| Solar recharge needed | 133 W |
- 1.
Usable_Wh = Nominal_Voltage × Capacity_Ah × DoD% - 2.
Days_Off_Grid = Usable_Wh / Daily_Wh - 3.
Solar_Watts_Needed = Daily_Wh / Peak_Sun_Hours
How to Use This Calculator
1. Enter your details
Use the labelled fields and units that match your situation.
2. Calculate instantly
The result, visual comparison, and working update as values change.
3. Review your result
Check assumptions, then copy, print, or share the calculation.
Formula & step-by-step maths
- DoD%
- Safe depth of discharge for battery chemistry
- Daily_Wh
- Sum of appliance watt-hours per day
Why depth of discharge changes everything
A 100Ah lead-acid battery only offers about 50Ah of usable capacity before damaging the battery, while the same-rated lithium LiFePO4 battery safely delivers 90Ah. This difference means lithium banks often need half the rated capacity to match lead-acid runtime.
Building an accurate daily Wh inventory
Sum each appliance's wattage times hours used per day — a 45W compressor fridge cycling 8 hours effectively draws about 360Wh, while phone chargers and LED lights typically add only 50-150Wh combined for a full day.
Sizing solar for recharge, not just storage
Solar sizing assumes roughly 4-5 peak sun hours per day in most US latitudes; cloudy days or steep panel angles reduce this significantly, so many installers add 20-30% extra panel wattage as a buffer.
Inverter sizing considerations
While this tool estimates runtime, always size your inverter's continuous wattage rating above your highest simultaneous appliance draw, and its surge rating above the highest single motor-start spike (like a compressor fridge or microwave).
Typical RV appliance daily Wh usage
| Appliance | Watts | Hours/day | Wh/day |
|---|---|---|---|
| 12V compressor fridge | 45W | 8h | 360Wh |
| LED lighting (4 lights) | 40W total | 4h | 160Wh |
| Laptop charging | 60W | 2h | 120Wh |
| Phone charging (2) | 10W | 3h | 30Wh |
| 12V TV | 30W | 2h | 60Wh |
| Water pump | 60W | 0.5h | 30Wh |
| Vent fan | 20W | 3h | 60Wh |
Frequently Asked Questions
Three worked examples
Same engine, three different starting points — useful if you want to see how sensitive the answer is before you type your own numbers in.
Example 1: battery bank capacity 78 Ah, battery type "AGM (60% DoD)"
On the lower / more conservative end. Your battery bank provides about 0.9 days off-grid at 600 Wh/day usage.
Example 2: battery bank capacity 100 Ah, battery type "Lithium LiFePO4 (90% DoD)"
A typical middle-of-the-road setup. Your battery bank provides about 1.8 days off-grid at 600 Wh/day usage.
Example 3: battery bank capacity 130 Ah, battery type "Lithium LiFePO4 (90% DoD)"
On the higher / more demanding end. Your battery bank provides about 2.3 days off-grid at 600 Wh/day usage.
Quick answers about the RV Battery Runtime
What exactly does the RV Battery Runtime work out?
Running out of power mid-trip is a common boondocking mistake because usable capacity is much lower than the printed amp-hour rating once depth of discharge is factored in. You enter battery type, battery bank capacity, nominal voltage and total daily appliance usage and the result panel updates straight away, so you can compare two or three versions of the same question in a few seconds.
What do I need before I start?
Only 4 fields: battery type, battery bank capacity, nominal voltage and total daily appliance usage. Nothing else is needed and nothing is stored.
How is it calculated — why depth of discharge changes everything?
A 100Ah lead-acid battery only offers about 50Ah of usable capacity before damaging the battery, while the same-rated lithium LiFePO4 battery safely delivers 90Ah. The same maths runs inside this page, so hand-checking the result on paper gives you the identical figure.
Why do two calculators give me different answers for rV Battery Runtime?
Sum each appliance's wattage times hours used per day — a 45W compressor fridge cycling 8 hours effectively draws about 360Wh, while phone chargers and LED lights typically add only 50-150Wh combined for a full day. Different sites pick different assumptions, so always check which method a calculator states before you trust the gap between two numbers.
What does the "Typical RV appliance daily Wh usage" table on this page tell me?
It is the reference range this tool works against — 7 rows from "12V compressor fridge" (45W) up to "Vent fan" (20W). Use it to sanity-check whether the number you just calculated sits where you expected it to.
Which battery type should I pick?
The dropdown offers 3 choices — Lead-Acid (50% DoD), AGM (60% DoD) and Lithium LiFePO4 (90% DoD). Pick the one that matches your real situation rather than the one you would like to be true; battery type usually moves the final figure more than any other single input, so it is worth running it twice with the option above and below your guess.
Do I have to press a button or reload the page to see the result?
No. RV Battery Runtime runs completely inside your browser, so the moment you change a value the cards recalculate — there is no submit step, no page reload and no waiting for a server round trip. That also means it keeps working on a weak or intermittent mobile connection.
Is it free, and do you keep what I type?
It is free with no sign-up, no app install and no usage limit. Nothing you enter into RV Battery Runtime leaves your device — the calculation is JavaScript running locally, so there is no upload of your figures to DrHint or anyone else.
Can I use it on a phone?
Yes — the layout stacks to a single column on small screens and the number fields open the numeric keypad on both Android and iOS. Many people bookmark this page or add it to their home screen and re-open it whenever the question comes up.
Anything to be careful about with the result?
Manufacturers rate total stored energy, but discharging batteries beyond their safe depth of discharge shortens lifespan dramatically, so usable capacity is always a fraction of the nameplate rating. Treat the output as a well-grounded estimate for planning, not as a professional, legal or medical decision on its own.
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