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Battery planning

Battery sizing calculator

Add the devices that actually run in your rig and size your battery bank around them instead of guessing from a product page.

Build around the day

The right bank is the one you can use and refill.

Capacity only helps if it matches your load list, usable depth, and charging routine. Start with the day you actually live, then let the bank size follow.

Daily use
1,410Wh
Required bank
300Ah
Next check
Recharge fit

Daily loads

What actually runs

Fridge duty cycle, fans, work gear, internet, CPAP, and small chargers matter more than the battery label.

Reserve days

How much cushion

Autonomy is the cloudy-day buffer, not a vanity number that makes the bank look tougher on paper.

Recharge path

Can you refill it?

Solar, alternator, generator, and shore charging decide whether a larger bank feels useful or stranded.

Start from a real battery planning profile
Custom plan

Battery sizing calculator

Add the loads you actually use in a normal day. The estimate updates as soon as the list changes.

The default profile starts with a 12V fridge, laptop, and lights so the tool has a realistic baseline. Replace those rows with your own appliances, then use the presets above if you want to compare a weekend, everyday, remote-work, or longer-reserve setup.

Battery bank estimate

Daily use

1410Wh

1580Wh with losses

Required capacity

300Ah

Usable storage

3.2kWh

12V 100Ah modules

3

Bank read

Everyday off-grid bank

A more serious battery target for frequent boondocking, inverter use, and steadier comfort.

This layout assumes common 12V 100Ah building blocks, then arranges them into a 12V bank.

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This calculator stores inputs locally in this browser. Clear saved inputs when stale values are getting in the way.

Shareable plan previewReview the saved checklistOpen the longer checklist only when you need copy, export, or print details.

A printable battery-bank snapshot that turns the appliance list into storage, layout, monitoring, and recharge decisions.

Quick answer

Recommended battery setup

Balanced everyday bank

Buying guidance

$2,200-$6,050

  • The largest loads are 12V fridge, Laptop, Lights; verify those hours before buying batteries.
  • Keep the charger, monitor, fusing, and wire path in the same plan as the batteries so the bank can actually recover.

Assumptions and confidence

  • Make sure the battery compartment can handle the module count, cable routing, ventilation needs, and service access.
  • Match the converter, solar controller, DC-DC charger, and battery monitor to the chosen chemistry.
  • Verify BMS charge and discharge limits against inverter surge and expected charging current.

Biggest answer movers

  • Longer appliance runtimes raise the bank faster than most nameplate watt changes.
  • Switching chemistry changes usable depth of discharge and can reshape the whole bank.
  • Adding autonomy days increases storage even if daily use stays the same.

Planning boundary

This is a planning estimate. Final fuse sizing, cable sizing, enclosure design, and manufacturer installation limits still need a qualified check.

Assumptions to verify

Bank layout: 1S x 3P

135Ah/day at 12V, with +170Wh for inverter and system losses.

Chemistry: LiFePO4

2,500-4,000+ cycles at sensible depth of discharge. Match chargers, monitor settings, and BMS limits before buying.

12V fridge

51% of daily use

720Wh/day from 60W for 12h

Laptop

38% of daily use

540Wh/day from 90W for 6h

Lights

11% of daily use

150Wh/day from 30W for 5h

What-if checks Stress-test the battery estimate before you price it. The main card gives the bank target. These scenarios show what changes when runtimes drift, recharge weakens, or you add more reserve.

Check the bank before you price it

These scenarios show whether the battery answer still works when run-times drift longer, recharge gets weaker, or you add more buffer than the base case.

What-if scenarios

Current use

Base bank

The closest match to the appliance list and autonomy target you entered.

Daily use

1,410Wh

Bank

300Ah

Modules

3 x 12V 100Ah

Heavier day

20% longer runtime

Useful when the listed appliances often run longer than the average paper estimate.

Daily use

1,692Wh

Bank

375Ah

Delta

+1 modules

Storm buffer

One more autonomy day

The cleaner way to buy reserve when recharge quality is the limiting factor, not the daily load list.

Bank

450Ah

Layout

1S x 5P

Usable

4.9 kWh

Biggest answer movers

Largest daily load

12V fridge uses 51%

720Wh/day from 60W for 12h.

Add 1 buffer day

+2 modules

Extra autonomy usually costs fewer dollars than oversizing everything else in the system.

Switch to AGM

+250Ah

Chemistry changes usable depth enough that it meaningfully reshapes the bank size, not just the price.

Build paths Compare battery builds after the load list is honest. Keep product and cost detail collapsed until the daily loads, reserve target, and recharge plan all make sense together.

Three bank builds from your load list

Each plan clears the calculator target, but with a different balance of upfront cost, reserve capacity, and install effort.

Budget$2,200 estimate

Budget battery bank

This version buys the bank you need today, plus the core monitoring and protection gear that keeps the install usable.

Install difficulty
Moderate
Time
Half-day swap

Cost model

$2,200 planned total
Battery modules
$1,650
3 x 12V 100Ah LiFePO4 modules for the bank layout.
Battery monitor
$150
Shunt-based state-of-charge monitoring allowance.
Recharge path
$225
Basic recovery allowance.
Protection and cabling
$200
Main fuse, busbar, lugs, heat shrink, and heavy battery cable allowance.

Planning estimate reviewed April 2026. Merchant pricing, coupons, freight, and availability can move quickly, so confirm the linked product pages before buying.

Best fit

Best for 12v fridge + laptop days when you want the bank to meet the current math without paying for future expansion now.

Parts list

Why it fits

  • The bank size is intentionally matched to 12v fridge + laptop days, not just the total watt-hours on paper.
  • If you expect colder travel or more inverter use than this profile shows, the budget bank will feel closest to the next tier up in real life.
Balanced$2,950 estimate

Balanced everyday bank

This build adds one layer of reserve and a stronger charging/monitoring path so the bank feels easier to live with between recharge cycles.

Install difficulty
Moderate
Time
Weekend retrofit

Cost model

$2,950 planned total
Battery modules
$2,100
3 x 12V 100Ah LiFePO4 modules for the bank layout.
Battery monitor
$225
Shunt-based state-of-charge monitoring allowance.
Recharge path
$400
Stronger solar, alternator, or charger recovery allowance.
Protection and cabling
$275
Main fuse, busbar, lugs, heat shrink, and heavy battery cable allowance.

Planning estimate reviewed April 2026. Merchant pricing, coupons, freight, and availability can move quickly, so confirm the linked product pages before buying.

Best fit

Best for frequent off-grid nights and mixed inverter loads where a little extra reserve reduces daily charge anxiety.

Parts list

Why it fits

  • The bank size is intentionally matched to 12v fridge + laptop days, not just the total watt-hours on paper.
  • If you expect colder travel or more inverter use than this profile shows, the balanced bank will feel closest to the next tier up in real life.
Premium$6,050 estimate

Premium reserve bank

This version spends more on reserve and supporting gear so voltage sag, cold-weather recharge friction, and overnight draw are less disruptive.

Install difficulty
Advanced
Time
Weekend plus tuning

Cost model

$6,050 planned total
Battery modules
$4,625
5 x 12V 100Ah LiFePO4 modules for the bank layout.
Battery monitor
$325
Shunt-based state-of-charge monitoring allowance.
Recharge path
$650
Stronger solar, alternator, or charger recovery allowance.
Protection and cabling
$425
Main fuse, busbar, lugs, heat shrink, and heavy battery cable allowance.

Planning estimate reviewed April 2026. Merchant pricing, coupons, freight, and availability can move quickly, so confirm the linked product pages before buying.

Best fit

Best for heavy workday loads, weather swings, and travelers who want reserve capacity before the load list inevitably grows.

Parts list

Why it fits

  • The bank size is intentionally matched to 12v fridge + laptop days, not just the total watt-hours on paper.
  • If you expect colder travel or more inverter use than this profile shows, the premium bank will feel closest to the next tier up in real life.

Not sure whether the result fits your exact rig?

Send this setup as a reader question so it can become a Q&A answer or future calculator example.

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More context Use one follow-up path instead of another pile of open tabs. Open this when you want margin options or the guide path that matches the current estimate.

How the battery target changes with more or less cushion

Tight margin

225Ah

Works if solar or alternator recovery is strong and heavy loads stay disciplined.

Balanced

300Ah

Closest to the assumptions and autonomy target you entered above.

More cushion

400Ah

Friendlier when your workday, weather, or overnight loads are less predictable.

Best next guides from this result

Read the battery-bank sizing guide

See how runtime, chemistry, and recharge speed affect the final bank choice.

Read the battery bank sizing guide

Compare lithium vs AGM

Make sure the battery chemistry matches the way you actually use the rig.

Compare lithium and AGM batteries

Check the battery monitor guide

Understand how to track state of charge once the bank is installed.

Read the RV battery monitor guide
Compare battery builds

Battery math

How the battery calculator turns loads into a bank

The result starts with appliance-by-appliance daily use, then adds autonomy, chemistry, voltage, inverter/system losses, and practical bank-building constraints.

Daily load

Each appliance is watts times hours per day. The calculator totals those rows before applying autonomy and loss assumptions.

Usable reserve

Required reserve is daily watt-hours times buffer days, with a system-loss allowance so inverter and wiring losses are not ignored.

Amp-hours

Amp-hours are watt-hours divided by bank voltage, then adjusted for lithium or AGM usable depth of discharge.

Avoid these traps

Common mistakes before buying

Buying one battery at a time

Whole-bank math matters. Mixing ages, capacities, or product lines can create imbalance and make future expansion awkward.

Ignoring recharge speed

A large bank that cannot be refilled by solar, alternator, or shore power becomes expensive ballast after a few cloudy days.

Overbuilding parallel strings

Many 12V lithium banks get messy above four parallel batteries. Larger builds may deserve 24V or 48V planning.

Treat the calculator result as a planning range, then verify the relevant manufacturer guidance, safety limits, installation requirements, and local rules before changing the rig.See assumptions

Gear to compare after the math

Spec-checked products to compare after the math.

These handoffs match the calculator family, not a one-click prescription. Verify fit, specs, clearances, and install limits before buying.

SOK SK12V100P 12V 100Ah LiFePO4 Battery

Best for

Budget lithium builds after a smaller bank result

A common 100Ah building block when the calculator result still fits a straightforward 12V lithium bank.

Current listing

SOK SK12V100P 12V 100Ah LiFePO4 Battery at SOK.

Checked model
SK12V100P
Spec fit
A 100Ah LiFePO4 building block for smaller 12V banks when the calculator result is framed around modular battery count and charger compatibility.
Check battery priceMerchant link. Direct merchant or retailer listing.

Victron SmartShunt 500A/50mV

Best for

Making battery runtime visible instead of guessed

A shunt-based monitor is the usual next buy when the calculator result depends on real state-of-charge tracking.

Current listing

Victron SmartShunt 500A/50mV at Victron.

Checked model
SmartShunt 500A/50mV
Spec fit
A shunt-based monitor handoff when calculator results depend on real state-of-charge and consumed amp-hours instead of voltage guessing.
Check monitor priceMerchant link. Direct merchant or retailer listing.

Victron Orion XS 12/12-50A DC-DC Battery Charger

Best for

Improving recharge support for larger daily loads

Use this class of DC-DC charger when the battery answer only works if drive-day recovery is part of the plan.

Current listing

Victron Orion XS 12/12-50A DC-DC Battery Charger at Victron.

Checked model
Orion XS 12/12-50A
Spec fit
A 50A DC-to-DC charger handoff when route-day charging is part of the battery recovery plan and alternator reserve is verified.
Check charger priceMerchant link. Direct merchant or retailer listing.

Frequently asked

Questions RVers usually ask next.

Why does lithium need fewer listed amp-hours than AGM?

Lithium batteries usually allow a much deeper usable discharge, hold voltage better under load, and recharge faster. AGM banks should be sized larger because less of the listed capacity is practical to use regularly.

When should I consider 24V or 48V instead of 12V?

Consider higher voltage when inverter loads, charge current, or battery count become large enough that 12V wiring and parallel strings get bulky or hard to protect cleanly.

Should I size the bank around the largest appliance?

Size battery capacity around daily watt-hours and autonomy. Size inverter and discharge limits around the largest simultaneous AC loads.