A 12V battery stores watt-hours (Wh), not watts — and the total depends on its amp-hour (Ah) rating. A 12V 100Ah battery stores 1,200 watt-hours (Wh) of energy. The watts it can deliver at any moment depend on the load connected to it: it can power a 100W device for 12 hours, a 600W device for 2 hours, or a 1,200W device for about 1 hour (minus efficiency losses).
The key distinction: watts = power (rate), watt-hours = energy (total). Read on for our calculator, a complete reference chart, and real-world examples.
12V Battery Watts Calculator
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The Two "Watts" Questions for 12V Batteries
People asking "how many watts in a 12V battery" usually mean one of two things:
Question 1: How Much Energy Does It Store? (Watt-Hours)
Formula: Wh = 12V x Ah
This tells you the total energy capacity. A 12V 100Ah battery stores 1,200 Wh — the energy equivalent of running a 100-watt light bulb for 12 hours.
Question 2: How Many Watts Can It Deliver? (Power Output)
Formula: W = V x A (at any given moment)
This depends on how much current (amps) you're drawing. The maximum continuous power depends on the battery's design and your inverter:
| Battery Type | Typical Max Continuous Amps | Max Watts at 12V |
|---|---|---|
| Car starter (flooded lead-acid) | 25-50A continuous | 300-600W |
| Deep cycle AGM | 50-100A continuous | 600-1,200W |
| Deep cycle LiFePO4 | 100-200A continuous | 1,200-2,400W |
| Inverter-limited | Depends on inverter | 300-3,000W |
Your inverter is usually the bottleneck. Even if a battery can deliver 200A (2,400W), your inverter must be rated for that wattage. A 1,000W inverter will limit output to 1,000W regardless of battery capability. Always match your inverter to your load requirements.
Complete 12V Battery Watt-Hours Chart
Standard 12V Batteries (by Amp-Hour Rating)
| Battery Size (Ah) | Watt-Hours (Wh) | Common Use | Approximate Weight |
|---|---|---|---|
| 5 Ah | 60 Wh | Alarm systems, small UPS | 3-4 lbs |
| 7 Ah | 84 Wh | UPS backup, emergency lights | 5-6 lbs |
| 9 Ah | 108 Wh | Security systems, small devices | 6-7 lbs |
| 12 Ah | 144 Wh | Mobility scooters, fish finders | 8-10 lbs |
| 18 Ah | 216 Wh | Electric wheelchairs, lawn mowers | 12-15 lbs |
| 20 Ah | 240 Wh | Portable power, trolling motors | 13-15 lbs |
| 35 Ah | 420 Wh | Medium trolling motors, backup | 22-26 lbs |
| 50 Ah | 600 Wh | RV house batteries, solar | 28-35 lbs |
| 75 Ah | 900 Wh | Marine deep cycle, larger solar | 42-50 lbs |
| 100 Ah | 1,200 Wh | RV/marine, off-grid solar | 28 lbs (LiFePO4) / 63 lbs (lead-acid) |
| 125 Ah | 1,500 Wh | Large RV systems | 35 lbs (LiFePO4) / 78 lbs (lead-acid) |
| 150 Ah | 1,800 Wh | Off-grid solar banks | 42 lbs (LiFePO4) / 95 lbs (lead-acid) |
| 200 Ah | 2,400 Wh | Heavy-duty off-grid, marine | 55 lbs (LiFePO4) / 120 lbs (lead-acid) |
| 300 Ah | 3,600 Wh | Large off-grid systems | 80 lbs (LiFePO4) |
LiFePO4 batteries weigh roughly half as much as lead-acid batteries at the same capacity — and you can use 80-100% of their rated capacity versus only 50% for lead-acid. A 100Ah LiFePO4 battery provides the same usable energy as a 200Ah lead-acid battery.
Usable Watts by Battery Chemistry
Not all watt-hours are actually usable. Depth of discharge (DoD) determines how much energy you can safely extract:
| Battery Chemistry | Rated Capacity | Total Wh | Usable DoD | Usable Wh |
|---|---|---|---|---|
| Flooded lead-acid | 12V 100Ah | 1,200 | 50% | 600 |
| AGM lead-acid | 12V 100Ah | 1,200 | 50-60% | 600-720 |
| Gel lead-acid | 12V 100Ah | 1,200 | 50-60% | 600-720 |
| LiFePO4 | 12.8V 100Ah | 1,280 | 80-100% | 1,024-1,280 |
This is why comparing batteries solely on Ah rating is misleading. A 100Ah LiFePO4 battery gives you twice the usable energy of a 100Ah flooded lead-acid battery.
How Long Will a 12V Battery Power My Device?
Runtime Formula
Runtime (hours) = Usable Wh / Device Watts x Inverter Efficiency
For a 12V 100Ah LiFePO4 battery (1,024 usable Wh) with a 90% efficient inverter:
| Device | Watts | Runtime |
|---|---|---|
| LED light bulb | 10W | 92 hours |
| Phone charger | 15W | 61 hours |
| Laptop | 45W | 20 hours |
| LED TV (50 inch) | 80W | 11.5 hours |
| Mini fridge | 60W (avg) | 15 hours |
| CPAP machine | 30-60W | 15-31 hours |
| Window fan | 75W | 12 hours |
| Portable heater | 750W | 1.2 hours |
| Space heater | 1,500W | 0.6 hours |
| Microwave | 1,000W | 55 minutes |
| Window AC (5,000 BTU) | 500W | 1.8 hours |
For the same 100Ah battery in lead-acid (600 usable Wh, 90% inverter):
| Device | Watts | Runtime (Lead-Acid) |
|---|---|---|
| LED light bulb | 10W | 54 hours |
| Phone charger | 15W | 36 hours |
| Laptop | 45W | 12 hours |
| LED TV (50 inch) | 80W | 6.8 hours |
| Mini fridge | 60W (avg) | 9 hours |
| CPAP machine | 30-60W | 9-18 hours |
CPAP users: A 12V 100Ah LiFePO4 battery is the gold standard for camping and travel CPAP backup. Most CPAP machines draw 30-60W, giving you 2-4 nights of use on a single charge. Use a DC-to-DC adapter (12V to CPAP native voltage) instead of an AC inverter to eliminate conversion losses and extend runtime by 15-20%.
Watts vs. Watt-Hours vs. Amp-Hours: A Clear Comparison
| Term | Unit | What It Measures | Analogy |
|---|---|---|---|
| Volts (V) | V | Electrical pressure | Water pressure |
| Amps (A) | A | Current flow rate | Water flow rate |
| Watts (W) | W | Power (rate of energy use) | Speed of a car |
| Amp-hours (Ah) | Ah | Charge capacity | Gas tank in gallons |
| Watt-hours (Wh) | Wh | Energy capacity | Gas tank x engine efficiency |
The relationships:
- W = V x A (power at any moment)
- Wh = V x Ah (total energy stored)
- Runtime = Wh / W (how long it lasts)
Real-World Examples
Example 1: Running an RV on 12V Batteries
You have two 12V 100Ah LiFePO4 batteries wired in parallel (total: 12V, 200Ah, 2,560 Wh usable). Your daily RV electrical load:
| Load | Watts | Hours/Day | Wh/Day |
|---|---|---|---|
| LED lights | 40W | 5 | 200 |
| Water pump | 60W | 0.5 | 30 |
| Phone/tablet charging | 30W | 3 | 90 |
| Laptop | 45W | 4 | 180 |
| Exhaust fan | 25W | 6 | 150 |
| 12V fridge | 45W (avg) | 24 | 1,080 |
| Total | 1,730 Wh/day |
With 2,560 Wh usable, your battery bank covers 1.5 days without recharging. A 400W solar panel in 5 peak sun hours generates 2,000 Wh/day, more than enough to keep the batteries topped off indefinitely.
Example 2: Emergency Sump Pump Backup
A 1/3 HP sump pump draws 800W while running. During a heavy storm, it cycles 10 minutes on, 20 minutes off. Your 12V 100Ah LiFePO4 battery (1,024 usable Wh) paired with a 1,500W inverter:
- Per-hour energy: 800W x (10/30) = 267 Wh per hour
- Runtime: 1,024 / 267 = 3.8 hours of storm protection
- For 12-hour protection, you would need three 100Ah batteries
Example 3: Tailgating and Outdoor Party Power
You are running a TV (80W), a blender (300W intermittent), a phone charging station (60W), and LED string lights (20W) for a 6-hour tailgate:
- Continuous load: 80 + 60 + 20 = 160W x 6 hours = 960 Wh
- Blender bursts: 300W x 0.25 hours total = 75 Wh
- Total: 1,035 Wh
- A single 12V 100Ah LiFePO4 battery (1,024 Wh usable) just barely covers it. A 150Ah battery provides comfortable headroom.
Example 4: Off-Grid Solar Cabin
A small off-grid cabin needs 3,000 Wh per day (lights, fridge, water pump, entertainment). With 2 days of autonomy for cloudy weather:
- Required storage: 3,000 x 2 = 6,000 Wh
- Using 12V 200Ah LiFePO4 batteries (2,048 Wh usable each)
- Batteries needed: 6,000 / 2,048 = 3 batteries in parallel
- Solar array: 1,200W or more (to recharge 3,000 Wh per day with about 5 sun hours)
12V Battery Configurations: Series vs. Parallel
When one 12V battery is not enough, you can combine multiple batteries:
Parallel (Same Voltage, More Capacity)
Connect positive to positive, negative to negative. Voltage stays at 12V, amp-hours add up.
| Configuration | Voltage | Total Ah | Total Wh |
|---|---|---|---|
| 1 x 12V 100Ah | 12V | 100 Ah | 1,200 Wh |
| 2 x 12V 100Ah parallel | 12V | 200 Ah | 2,400 Wh |
| 3 x 12V 100Ah parallel | 12V | 300 Ah | 3,600 Wh |
| 4 x 12V 100Ah parallel | 12V | 400 Ah | 4,800 Wh |
Series (More Voltage, Same Capacity)
Connect positive to negative in a chain. Amp-hours stay the same, voltage adds up. Used for 24V and 48V systems.
| Configuration | Voltage | Total Ah | Total Wh |
|---|---|---|---|
| 2 x 12V 100Ah series | 24V | 100 Ah | 2,400 Wh |
| 4 x 12V 100Ah series | 48V | 100 Ah | 4,800 Wh |
Never mix old and new batteries, or different brands and chemistries, in series or parallel. Mismatched batteries cause uneven charging, reduced capacity, and potential safety issues. If you need to expand, buy identical batteries from the same manufacturer and batch.
Choosing the Right 12V Battery for Your Application
| Application | Recommended Type | Min Ah | Min Wh | Typical Budget |
|---|---|---|---|---|
| UPS / alarm backup | AGM lead-acid | 7-12 Ah | 84-144 Wh | $20-$40 |
| Fish finder / trolling motor | AGM or LiFePO4 | 35-100 Ah | 420-1,280 Wh | $80-$400 |
| RV house battery | LiFePO4 | 100-200 Ah | 1,280-2,560 Wh | $300-$800 |
| Off-grid solar | LiFePO4 | 200+ Ah | 2,560+ Wh | $600-$1,600 |
| Marine deep cycle | AGM or LiFePO4 | 100-150 Ah | 1,200-1,920 Wh | $150-$600 |
| Emergency home backup | LiFePO4 | 100+ Ah | 1,280+ Wh | $300-$700 |
| CPAP travel battery | LiFePO4 | 50-100 Ah | 640-1,280 Wh | $200-$500 |
| Van life / mobile office | LiFePO4 | 200-300 Ah | 2,560-3,840 Wh | $700-$1,500 |
12V Battery Pricing Guide (2026)
| Battery | Chemistry | Capacity | Approx Price | Price per Wh |
|---|---|---|---|---|
| Universal Power UB12070 | AGM | 7Ah / 84Wh | $20-$25 | $0.24-$0.30 |
| VMAXTANKS SLR125 | AGM | 125Ah / 1,500Wh | $250-$300 | $0.17-$0.20 |
| Renogy 100Ah Smart | LiFePO4 | 100Ah / 1,280Wh | $280-$350 | $0.22-$0.27 |
| Battle Born BB10012 | LiFePO4 | 100Ah / 1,280Wh | $700-$800 | $0.55-$0.63 |
| Victron Smart 200Ah | LiFePO4 | 200Ah / 2,560Wh | $1,200-$1,500 | $0.47-$0.59 |
| SOK 206Ah Server Rack | LiFePO4 | 206Ah / 2,637Wh | $600-$750 | $0.23-$0.28 |
| EcoFlow Delta 2 Max | Li-ion (portable) | 160Ah equiv / 2,048Wh | $1,600-$2,000 | $0.78-$0.98 |
Best value in 2026: Budget LiFePO4 batteries from brands like Renogy, SOK, and Ampere Time now cost $0.20-$0.30 per Wh, approaching lead-acid AGM pricing while offering double the usable capacity and 5-10x the cycle life. Premium brands like Battle Born and Victron charge a premium for better BMS features and customer support.
How to Calculate Charging Time for a 12V Battery
Charging time (hours) = Battery Ah / Charger Amps x 1.1
The 1.1 multiplier accounts for charging efficiency losses. As a battery fills, the charge rate slows (especially the last 10-20%), so real-world charging takes longer than the formula suggests.
| Battery Size | 10A Charger | 20A Charger | 40A Charger | 100W Solar Panel |
|---|---|---|---|---|
| 50 Ah | 5.5 hrs | 2.75 hrs | 1.4 hrs | 6-8 hrs |
| 100 Ah | 11 hrs | 5.5 hrs | 2.75 hrs | 12-16 hrs |
| 200 Ah | 22 hrs | 11 hrs | 5.5 hrs | 24-32 hrs |
| 300 Ah | 33 hrs | 16.5 hrs | 8.25 hrs | 36-48 hrs |
Solar panel charging time assumes 5 peak sun hours and 8-10A effective charging current from a 100W panel.
Key Takeaways
- Watt-hours formula: Wh = 12V x Ah. A 100Ah battery stores 1,200 Wh total
- Usable energy depends on chemistry. Lead-acid gives you 50% (600 Wh), LiFePO4 gives you 80-100% (1,024-1,280 Wh)
- Runtime = Usable Wh / Device Watts x 0.9 (accounting for inverter losses)
- LiFePO4 is the clear winner for most applications with 2x usable energy, half the weight, and 5-10x the lifespan of lead-acid
- Match your inverter to your load. The battery can only deliver what the inverter allows
- For whole-home backup, consider dedicated home batteries (Powerwall, Enphase, Franklin) instead of DIY 12V setups
Frequently Asked Questions
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