Quick Answers
The amp-hour capacity needed for an RV battery depends on several factors, including:
- The size and electrical load of the RV
- How long you need the battery to last between charges
- Whether you have shore power available or will be dry camping
- The number and type of batteries in your setup
As a general guideline, most RVs will need 200-400 amp-hour capacity to safely run lights, appliances and accessories for short periods. For extended dry camping, 600-1000+ amp-hours may be required.
Determining the right battery amp-hour capacity for your RV involves understanding your specific power needs and usage. With the proliferation of electrical devices and appliances in modern RVs, an adequately sized battery bank is crucial. You want to be sure your batteries can comfortably support all lighting, refrigeration, entertainment and other electrical loads – especially when dry camping without shore power.
In this article, we’ll cover the key factors that determine RV battery amp-hour requirements. We’ll provide guidelines and examples for calculating your RV’s electrical load. You’ll also learn how to select the appropriate battery capacity for different types of RV camping and usage profiles.
What Are Amp-Hours?
Before jumping into RV battery sizing, it’s helpful to understand what “amp-hours” means. An amp-hour is a unit of electric charge stored in a battery. Specifically, it is the amount of current (in amps) that a battery can provide for one hour.
For example, a 100 amp-hour battery could theoretically:
- Supply 5 amps for 20 hours
- Supply 10 amps for 10 hours
- Supply 20 amps for 5 hours
In reality, the usable capacity is less than the theoretical due to inefficiencies in charging and discharging. Nonetheless, amp-hour ratings allow easy comparison of different batteries’ capacities.
Key Factors in Determining RV Battery Size
Choosing the right amp-hour rating for your RV battery bank depends on several interrelated factors:
RV Size and Electrical Load
Larger RVs with more hardwired electrical loads will require more battery capacity. Standard items drawing power in an RV include:
- Lights
- Furnace
- Refrigerator
- Water pump
- Vent fans
- Propane detector and CO monitor
- LP leak detector
- Fantastic vent fan
In addition, most RVs will have various plugin appliances and electronics:
- TVs
- Computers and routers
- Coffee maker
- Microwave
- AC outlets
- Gaming consoles
- Cell phone and device chargers
Larger RVs like Class A motorhomes have more hardwired loads and ability to run more plugin devices. Small travel trailers have more modest power needs.
Dry Camping vs Shore Power
Your battery capacity needs will depend greatly on whether you have shore power available or intend to “dry camp” off-grid.
With shore power, a dedicated power converter can run accessories and appliances directly – conserving battery capacity for short term use between sites.
Dry camping requires relying completely on your RV battery bank to run all electrical loads. This demands increased battery capacity to avoid prematurely draining them.
Length of Time Off-Grid
How long do you plan to continuously run your RV off its batteries? Capacity requirements increase the longer you need battery power between charges. A few days off-grid requires a much larger battery bank than just overnight.
Battery Chemistry Type
Not all RV batteries are created equal. The three main types used are:
- Flooded lead-acid – Inexpensive but very heavy. Require maintenance.
- AGM – Absorbed glass mat design is lighter, more efficient and maintenance-free.
- Lithium-ion – Most expensive but lightest weight, highest performance and longest lasting.
Moving to lithium batteries can potentially allow reducing your battery bank’s total amp-hour capacity due to their superior efficiency and discharge capabilities.
Wiring System Voltage
Most RVs operate on a 12-volt DC system. But some larger motorhomes now use 24-volt or even 48-volt architecture. Higher voltage systems can effectively deliver more power with smaller, lighter wiring gauge. The voltage system impacts battery bank size and configuration.
Single vs Multiple Batteries
You can meet your RV’s amp-hour needs either with one large battery, or by wiring together a “bank” of two or more smaller batteries. The former requires a very high capacity (and expensive) single battery. The latter allows mixing and matching smaller batteries cost effectively.
Calculating Electrical Load
Figuring your RV’s amp-hour usage requires tallying all the electrical loads from lights, appliances, electronics and accessories. There are a couple approaches to this: Simple or Comprehensive.
Simple Load Calculation
A quick and rough way to estimate your RV battery needs is to:
- Count the number of coach lights
- Estimate the number of hours per day you’ll run lights and accessories off battery
- Multiply lights x hours to get “lighting amp-hours”
- Add flat amounts for other loads like fridge, furnace, water pump
For example:
- 8 interior coach lights at 1.5 amps = 12 amp-hours
- 4 exterior coach lights at 1.5 amps = 6 amp-hours
- Lights on for 4 hours = 18 + 12 = 30 amp-hours
- Add fridge (3 amp-hours), furnace (5 amp-hours), water pump (2 amp-hours)
- Total Estimated Load = 40 amp-hours
This approach gives you a ballpark figure for basic load. You’ll need to add any other loads like vent fans, electronics, appliances to get a better estimate.
Comprehensive Load Calculation
A more thorough approach is to inventory all installed electrical loads and usage time to build a complete amp-hour load profile. This can be tedious but provides a highly accurate number for proper battery sizing.
Follow these steps:
- Inventory all hardwired loads
- Document load amps for each item
- Estimate typical daily “on” time for each item
- Multiply amps x time to calculate amp-hours
- Total the amp-hour loads for all items
Here is an example comprehensive load table for a sample RV:
| Load Item | Amps | Daily Hours | Amp-Hours |
| Interior Lights | 1.5 | 4 | 6 |
| Exterior Lights | 1.5 | 2 | 3 |
| Fridge | 3.2 | 24 | 76.8 |
| Furnace | 5 | 2 | 10 |
| Water Pump | 7 | 0.5 | 3.5 |
| TV | 2 | 3 | 6 |
| Laptop | 1.5 | 2 | 3 |
| Coffee Maker | 6 | 0.5 | 3 |
| Total | 111.3 |
This provides a detailed load profile with precise expected amp-hour consumption. You now have the information for properly sizing your battery bank.
RV Battery Amp-Hour Requirements
Now that you understand the key variables and how to calculate electrical load, we can discuss some general guidelines and ranges for RV battery bank capacity.
Basic 12V System
On a basic 12-volt RV electrical system:
- 50-100 amp-hours supports very light usage for short trips or overnight camping with shore power available.
- 100-200 amp-hours works for simple weekend camping with prudent use of lights and accessories.
- 200-400 amp-hours lets you comfortably run most lights, fridge, electronics and small appliances for a few days.
- 400+ amp-hours provides capacity for moderate loads on extended trips of up to week off-grid.
Large and Luxury RVs
Larger motorhomes and fifth wheels with higher electrical loads often need upwards of:
- 500-800 amp-hours for a week’s dry camping
- 800-1000+ amp-hours for extended boondocking of two weeks or longer
Minimum Usable Capacity
Regardless of your calculated load, most experts recommend a minimum battery capacity of at least 200-300 amp-hours for any RV intended for overnight dry camping. This provides a safety margin and usable power to run basic lighting and fridge through the night.
General Rules of Thumb
Some general guidelines RV owners also use for battery sizing are:
- Small travel trailer: 200-400 amp-hour capacity
- Mid-size travel trailer or 5th wheel: 400-600 amp-hour capacity
- Large 5th wheel or Class C: 600-800 amp-hour capacity
- Class A motorhome: 800-1000+ amp-hour capacity
You’ll need to compare these benchmarks against your actual calculated load. But they provide a quick starting point.
Wiring Batteries Together
Once you’ve determined your ideal amp-hour capacity, you need to select and install the appropriate batteries. A few key wiring considerations:
Parallel vs Series
- Parallel: Batteries connected in parallel combine their amp-hour capacities. Voltage stays the same.
- Series: Batteries in series combine their voltages. Total amp-hours remain the same.
For RV applications, you almost always want batteries wired in parallel to increase total amp-hours. Do NOT series wire batteries in an RV unless you know specifically what you are doing.
Matched Batteries
When wiring two or more batteries in parallel, use identical or very close capacity batteries. This allows them to be charged and discharged evenly. Mixing very different amp-hour sizes can overload the smaller battery.
Battery Isolator
Use a battery isolator when connecting an auxiliary battery or trailer battery to your starter battery. This prevents draining your starter battery when using the house batteries.
Battery Management System
For more advanced battery installations, consider a Battery Management System (BMS). A BMS monitors your battery bank and helps:
- Provide precise readings on amp-hours remaining
- Prevent overcharging and over-discharging
- Allow safely connecting multiple batteries
- Identify bad or failing batteries
Quality BMS systems also offer improvements in charging efficiency, extended battery life, and automatic switching from starter to house or alternate charging sources.
Recharging Your Batteries
Your RV battery capacity needs factor in how long you can reasonably run from batteries, and how/where you will recharge them. Options include:
- Generator – onboard generators can charge batteries, but consume fuel
- Solar – solar panels to charge batteries work well for dry camping
- Alternator – alternator recharges when driving, but is slow
- Shore Power – best option when you have electric hookup in a campground
- Portable Charger – carry along a portable solar panel or charge pack for emergencies
Having multiple charging sources provides redundancy. Size batteries based on worst case discharge needs between opportunities to recharge.
RV Battery Sizing Recap
RV battery capacity is a prime factor in powering your RV effectively. With the right amp-hour battery bank, you can minimize generator runtimes, have power reserves in emergencies, and camp wherever you want.
The main steps for determining your RV battery needs are:
- Estimate your RV’s typical electrical loads
- Factor in any large temporary loads
- Decide how long you need to run between charging
- Select batteries to meet your amp-hour requirements
- Use multiple batteries in parallel if needed
- Consider a battery management system
- Make sure to have charging sources available
Every RV’s usage profile and needs are different. Do your homework to find the ideal total amp-hour capacity for your situation. Invest in robust deep cycle batteries from quality manufacturers. With adequate battery power on board, you’ll enjoy off-grid RV camping adventures for years to come.
