First, what’s an Ah?
Amp-hours (Ah) are like “gallons in a tank,” but for electricity.
If you use 10 Ah, you’ve used ten “gallons” from your battery. A 100Ah battery is a 100-gallon tank.
Daily Use & “Refill” Planner
Assumptions that keep this honest:
• Fridge ≈ 30 Ah/day (Dometic CFX3 35/45) • Fan (night on medium) ≈ 10 Ah • Lights ≈ 4 Ah
• “Good-sun day” = a solid sunny day with decent panel angle
• Usable battery: ~80% (leave ~20% in reserve)
| Camping day type | What’s in use | Energy used (Ah/day) | How long your battery lasts with no charging | To put that energy back (replace one day’s use) |
|---|---|---|---|---|
| Light Use | Fridge + lights | 34 Ah | 100Ah batt: ~2.4 days • 300Ah batt: ~7.1 days | Solar 1×100W: ~1.2 good-sun days • Solar 2×100W: ~0.6 good-sun days • Shore (PD4045KA): ~0.9 hr plugged in • Vehicle (8A DC-DC): ~4.2 hr driving |
| Typical Use | Fridge + fan (night, med) + lights | 44 Ah | 100Ah: ~1.8 days • 300Ah: ~5.5 days | Solar 1×100W: ~1.5 good-sun days • Solar 2×100W: ~0.8 good-sun days • Shore (PD4045KA): ~1.2 hr • Vehicle (8A DC-DC): ~5.5 hr |
| Hot Day | Fridge working harder + fan higher/longer + lights | 57 Ah | 100Ah: ~1.4 days • 300Ah: ~4.2 days | Solar 1×100W: ~2.0 good-sun days • Solar 2×100W: ~1.0 good-sun day • Shore (PD4045KA): ~1.5 hr • Vehicle (8A DC-DC): ~7.1 hr |
Rule-of-thumb outputs (what reaches the battery):
• Solar 1×100W: ~28.5 Ah per good-sun day • Solar 2×100W: ~57 Ah per good-sun day
• Shore – PD4045KA (45A): ~38 Ah per hour (real-world) • Vehicle – DC-DC (8A): 8 Ah per hour
Full recharge (from ~20% back to 100%)
Includes a little extra time for the final top-off.
| Battery | Energy to add | Solar 1×100W | Solar 2×100W | Shore – PD4045KA | Vehicle – 8A DC-DC |
|---|---|---|---|---|---|
| 100Ah lithium | ~80 Ah | ~3.1 good-sun days | ~1.5 good-sun days | ~2.3 hours plugged in | ~11 hours driving |
| 300Ah lithium | ~240 Ah | ~9.3 good-sun days | ~4.6 good-sun days | ~7.0 hours plugged in | ~33 hours driving |
Quick planning tips
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Two 100W panels can keep up with most warm-weather days; one panel pairs nicely with light use.
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Shore power (PD4045KA) is your fastest top-off: think ~38 Ah back per hour.
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Driving helps: the 8A DC-DC returns about 8 Ah for every hour the engine is running.
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Bigger battery = bigger buffer between sunny plugs-in or drive days.
All numbers are estimates—weather, shade, temps, and how you use the fan/fridge will swing real-world results.