100Ah vs 200Ah vs 300Ah: Which Battery Bank Size Do You Need?
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100Ah vs 200Ah vs 300Ah is the sizing question that decides most of your budget, and it is genuinely answerable with arithmetic rather than guesswork. The trick is converting amp-hours into watt-hours first, because amp-hours alone tell you nothing until you know the voltage.
The short answer
At 12 V, 100 Ah is 1,280 Wh, 200 Ah is 2,560 Wh and 300 Ah is 3,840 Wh. Weekend camping with light loads is a 100 Ah job. Extended boondocking with a compressor fridge wants 200 Ah. Full-time living, or anything running an inverter hard, starts at 300 Ah.
Convert to watt-hours before you compare anything
Amp-hours are voltage-dependent, which makes them useless for comparison on their own. Multiply amp-hours by nominal voltage to get watt-hours, and everything becomes comparable.
| Capacity | At 12.8V | At 25.6V | Typical weight |
|---|---|---|---|
| 100 Ah | 1,280 Wh | 2,560 Wh | ~25 lbs |
| 200 Ah | 2,560 Wh | 5,120 Wh | ~48 lbs |
| 300 Ah | 3,840 Wh | 7,680 Wh | ~70 lbs |
Note the LiFePO4 nominal voltage of 12.8 V rather than 12.0 V. Weights are typical for drop-in LiFePO4 and vary by manufacturer. Full method in watt-hours explained.
What 100Ah vs 200Ah vs 300Ah actually runs
Comparing 100Ah vs 200Ah vs 300Ah is easiest against real loads. These figures assume LiFePO4, which tolerates near-full discharge. If you are still on lead-acid, halve everything — you can only safely use about 50% of the rated capacity.
| Load | 100Ah | 200Ah | 300Ah |
|---|---|---|---|
| 12V compressor fridge (~40W avg) | ~27 hrs | ~54 hrs | ~82 hrs |
| LED lighting (~15W) | ~72 hrs | ~145 hrs | ~218 hrs |
| CPAP, no humidifier (~30W) | ~36 hrs | ~72 hrs | ~109 hrs |
| Laptop + router (~80W) | ~13 hrs | ~27 hrs | ~41 hrs |
| Induction hob (~1,500W) | ~45 min | ~1.5 hrs | ~2.2 hrs |
Figures include roughly 15% real-world loss. Anything running through an inverter loses more than a native 12 V appliance doing the same job, which is why 12 V fridges beat household fridges in vans by a wide margin.
Choosing between 100Ah vs 200Ah vs 300Ah
100 Ah suits weekend campers, tent and car campers, anyone with shore power most nights, and builds where lighting, charging and a fan are the whole load. It is also the right starting point if you have solar and only need to bridge overnight.
200 Ah suits most serious van and trailer builds. It runs a compressor fridge continuously, supports a modest inverter, and gives two to three days of autonomy without sun. This is the size most people should buy, and the one most people wish they had bought after starting at 100 Ah.
300 Ah suits full-timers, anyone cooking electrically, anyone running air conditioning even briefly, and cold-climate builds where solar production collapses for months. It is also the practical minimum if you want to run a 3,000 W inverter at anything near its rating.
The three things that change the answer
Solar changes it most. A 200 Ah bank with 400 W of solar behaves like a much larger bank without it, because it refills daily. Battery capacity buys you autonomy through dark days; solar buys you indefinite operation in good weather. Most builds are better served spending marginal money on panels than on a third battery.
Discharge rate limits matter as much as capacity. A 100 Ah battery with a 100 A BMS limit cannot support a 2,000 W inverter, which needs roughly 175 A. You would need two in parallel regardless of whether you need the extra energy — see battery bank wiring.
Weight and space are real constraints. 300 Ah is around 70 lbs and needs somewhere secure to live. In a van that is manageable; in a small trailer with tongue weight limits it may not be.
For appliance consumption figures to base your own calculation on, the ENERGY STAR database lists annual kilowatt-hour ratings by category.
Frequently asked questions
Is one 200Ah battery better than two 100Ah?
A single 200 Ah unit is simpler, usually lighter than two separate cases, and avoids parallel balancing concerns. Two 100 Ah units are easier to carry individually, fit awkward spaces, and give redundancy if one fails. Check the combined BMS current limit either way.
Can I use the full rated capacity of LiFePO4?
Very nearly. LiFePO4 handles deep discharge well, and most manufacturers rate cycle life at 80–100% depth of discharge. Plan on using about 90% of rated capacity in practice, leaving margin for BMS cutoff and cold-weather losses.
Should I buy bigger than I need now?
Somewhat, yes. Adding a battery to an aged bank underperforms because the new unit is pulled toward the condition of the old ones. If you expect your needs to grow, buying the larger size at the start generally works out better than expanding later.
How much solar matches each bank size?
A rough guide is 1–2 W of panel per amp-hour of battery: 100–200 W for 100 Ah, 200–400 W for 200 Ah, 300–600 W for 300 Ah. Go toward the upper end in winter, at high latitude, or with significant shading.
Last updated: July 20, 2026. Runtime figures are calculated estimates including a 15% efficiency allowance; actual results vary with temperature and load profile.