Backup Power Basics

What this guide covers

• Volts, amps, watts, and watt-hours in plain language
• Power banks versus portable power stations
• Charging priorities when grid power is out
• Runtime estimates and realistic solar limits
• Battery storage, heat, and fire safety
• Generator carbon monoxide warnings

Four numbers that actually matter

Electricity is water in a pipe, imperfectly. Volts (V) are pressure — household outlets in the US are about 120 V. Amps (A) are flow rate — how much current moves. Watts (W) are work done: watts equals volts times amps. A phone charger might say 5 V and 3 A, which is 15 W.

Watt-hours (Wh) are capacity — how long you can sustain a load. A 500 Wh battery running a 50 W load lasts roughly ten hours in theory. Real life adds losses: inverters, heat, and battery chemistry cut effective capacity by 10–25%. Plan on the pessimistic side.

Milliamps (mAh) on small power banks are not directly comparable across voltages without conversion. A 10,000 mAh bank at 3.7 V holds about 37 Wh. Divide device need by usable Wh to estimate charges, not marketing “phone charges” on the box.

Power banks versus portable power stations

Power banks are small lithium packs for USB devices — phones, earbuds, small fans. They are cheap, pocketable, and limited to low voltage DC output. Good for daily carry and short outages affecting communication only.

Portable power stations are larger batteries with multiple outputs — USB, 12 V DC, and often a 120 V AC inverter outlet. They run laptops, lamps, CPAP machines (check manufacturer draw), and small appliances under their rated continuous wattage. Weight and cost scale with Wh capacity.

Car inverters clip or wire to a 12 V socket and convert battery to 120 V AC. They work in a pinch but drain the vehicle starter battery fast if the engine is off. Idling the engine to charge devices wastes fuel and creates exhaust risk — charge while driving or use a separate pack.

Charging priorities when power is scarce

List devices by function, not sentiment. Tier 1: communication — phone, mobile hotspot, emergency radio. Tier 2: light — headlamp and one area lamp beat ceiling fixtures. Tier 3: work or income — laptop if your job depends on it. Tier 4: comfort — fans, entertainment, coffee makers.

Medical devices override the list — CPAP, insulin pumps, and powered mobility equipment need confirmed runtime with your physician’s input and manufacturer specs. Keep medical loads on dedicated circuits or packs when possible.

Charge Tier 1 fully before topping comfort devices. Airplane mode and lower screen brightness extend phone life more than carrying three extra banks you never charged. One cable per device type reduces loss and confusion.

Estimating runtime without guesswork

Step one: find each device’s watt draw — on the label, charger, or manufacturer site. Step two: add loads you will run at the same time. Step three: divide battery Wh (after 20% haircut) by total watts.

Example: a 720 Wh station with 20% loss leaves ~576 Wh usable. A 40 W laptop and 10 W LED lamp draw 50 W combined. 576 ÷ 50 ≈ 11.5 hours. Startup surges from motors — fridges, pumps — exceed continuous ratings briefly; stations may shut off if surge exceeds inverter limit.

Phones use variable draw; expect three to six full charges from a mid-size station depending on phone size and efficiency. Laptops vary widely — 30 W ultrabooks vs. 100 W workstations change the math entirely.

Solar: useful supplement, not magic

Portable solar panels recharge stations slowly under ideal sun — clear sky, proper angle, panel rated wattage or higher. Cloud cover, window glass, shade from trees, and winter sun cut output sharply. A 100 W panel rarely delivers 100 W continuously; expect a fraction over the day.

Solar works best as daytime top-up while you use stored power at night. It does not replace capacity for medical overnight loads or multi-day storms unless paired with large storage and realistic expectations. Panel plus long cable plus charge controller matched to your station matters — mismatched connectors and voltages waste money.

Battery storage, heat, and fire risk

Lithium-ion batteries hate heat and puncture. Do not leave power stations in a closed car in summer sun. Do not charge under pillows or blankets. Use manufacturer cables; cheap DC cables with wrong polarity damage packs and can ignite.

Swollen batteries, hiss, or sweet chemical smell means stop use, isolate the device on non-flammable surface if safe, and follow local disposal guidance — not household trash. Smoke means evacuate and call fire services; lithium fires are not ordinary grease fires.

Generators and carbon monoxide

Gas generators belong outdoors, far from windows, doors, vents, and vehicle cabins — exhaust kills silently. Never run a generator in a garage, porch, tent, or vehicle. CO detectors in sleeping areas are cheap relative to the risk. Extension cords rated for load length and gauge carry power inside; the generator stays out.

Refuel only when cool. Store fuel in approved containers away from living space. Transfer switches for home tie-in require electrician installation — backfeeding a wall outlet endangers line workers and your wiring.

Common mistakes

• Buying the biggest station without adding device watt draws first
• Running a car inverter overnight with engine off — dead starter battery
• Idling a vehicle in an enclosed space to charge devices — CO exposure
• Expecting a 100 W solar panel to fully recharge a large station in one cloudy afternoon
• Chaining cheap off-brand batteries near sleeping areas
• Plugging space heaters or toasters into small inverters — trip, melt, or fire
• Operating generators near windows or inside garages

Related Practical Independence resources

• Vehicle Living Fundamentals
• Emergency Water Systems
• Personal Documents & Recovery System
• Communication During Outages