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Power Station Math: How to Calculate Which Portable Generator You Actually Need

ttop brands

2026-01-23

10 min read

Practical, calculator-style guide to total household wattage, convert to usable battery capacity, and pick discounted portable generators.

Stop Guessing: Calculate Exactly Which Portable Generator You Need (and Which Deal to Buy)

Hook: If you’re overwhelmed by specs, surge ratings and half-truths on listing pages, you’re not alone. Shoppers want verified discounts on authentic, warranty-backed power stations — not surprises when the lights go out. This guide gives you a practical, calculator-style walk-through to total household wattage, convert that to usable battery capacity, and pick a discounted model that actually meets your needs in 2026.

The 2026 context: why sizing matters now

Battery chemistry, inverter tech and market pricing changed fast through late 2025. LFP (LiFePO4) batteries and integrated smart inverters are now common in consumer-grade portable generators, giving better cycle life and safer long-term warranties. Retailers ran big holiday-to-new-year clearances, so early-2026 deals (like the Jackery HomePower 3600 Plus and the EcoFlow DELTA 3 Max flash sale) can be excellent time-to-buy opportunities — but only if the model fits your real power needs. This guide uses those live-deal examples to show how to do the math, compare true cost-per-Wh, and verify warranty/returns before you checkout.

Step 1 — List the devices you must run

Start by listing only the essentials you truly need during an outage. Typical prioritized lists for deal-minded shoppers include:

Refrigerator (fridge + freezer)
Medical devices (CPAP, oxygen concentrators)
Lights and phone charging
Router/modem and a laptop
Sump pump or well pump (if you need water)
Space heater or electric furnace fan (if needed — huge power draw)

Keep realistic running watt estimates next to each device. Use nameplate data or measure with a plug watt-meter. If unavailable, use these conservative averages for calculator work:

Refrigerator: 100–200W running, 600–1,200W starting (compressor surge)
Chest freezer: 100–300W running
Router/modem: 10–30W
LED lighting (entire house essentials): 40–150W
CPAP: 40–70W
Sump pump: 800–1,500W running, 2,000–3,000W starting
Microwave, coffee maker: 800–1,500W (avoid unless necessary)

Step 2 — Calculate continuous load and surge needs

Two numbers matter: continuous watts and surge (peak) watts.

Continuous load (W): Add the running watts for every device you plan to run simultaneously.
Surge (start) watts: Identify the highest motor or compressor start requirement. The power station must handle that peak for a few seconds.

Example household profiles

These example profiles help you see real calculations. Use the same formula with your own device list.

Profile A — Essentials: Fridge + lights + router

Fridge running: 150W (surge 800W)
Lights (LED) total: 80W
Router/modem: 20W

Continuous load: 150 + 80 + 20 = 250W
Surge requirement: 800W (from fridge)

Profile B — Small apartment backup

Fridge: 150W (surge 800W)
Laptop + router: 100W
Lights + phone charging: 100W
CPAP: 50W

Continuous load: 400W
Surge: 800W

Profile C — Larger home partial backup (no HVAC)

Fridge/freezer combined: 300W (surge 1,200W)
Sump pump (intermittent): 1,000W running (surge 2,500W)
Lights + devices: 200W

Continuous: 1,500W (when pump runs add that 1,000W)
Surge: 2,500W

Step 3 — Convert to required battery capacity (Wh) and runtime

Battery capacity is given in watt-hours (Wh) or amp-hours (Ah). Most portable power stations list Wh. Use this formula for expected runtime:

Runtime (hours) = (Battery Wh × Usable fraction × Inverter efficiency) ÷ Load (W)

Key factors:

Usable fraction — many LFP stations allow 90–95% DoD; older chemistries use 80% or less. Be conservative: use 0.80–0.90 if you want long life.
Inverter efficiency — typically 85–95%. Use 0.88 as a safe middle-ground for mixed loads.

Worked example — Profile A (250W continuous)

Assume you want 12 hours of runtime for essentials. Required usable Wh = 250 W × 12 h = 3,000 Wh.

Accounting for efficiency and DoD conservatively:

Needed battery nominal Wh = 3,000 ÷ (0.80 × 0.88) ≈ 4,261 Wh.

So you need a station with at least ~4,300 Wh nominal capacity unless you plan to run fewer hours.

Quick conversion: Wh to Ah (if you have Ah specs)

Ah = Wh ÷ Voltage. Example: a 4,000 Wh pack at 51.2 V ≈ 78 Ah. Many portable packs use 12V, 24V or 51.2V battery stacks — the math is the same; just confirm the pack nominal voltage.

Step 4 — Account for surge capacity and simultaneous device starts

Always match both continuous and surge specs. If your fridge needs 1,200W start and your sump pump may start at 2,500W, the power station must support the higher surge. If no single station meets both surge and Wh needs at your price point, consider:

Staggering start times (don’t start pump and fridge simultaneously)
Adding a small secondary battery or inverter purely for surge support
Choosing a station with a high continuous inverter rating and a strong peak rating

Step 5 — Compare real deals using cost-per-Wh and features

Deals are great — but check the effective price per usable Wh, warranty, return window, and seller. Use this quick formula:

Effective $/Wh = Price ÷ (Advertised Wh × Usable fraction)

Example deal snapshots from early 2026:

Jackery HomePower 3600 Plus — advertised 3,600 Wh (nominal). Deal price example: $1,219 (solo) or $1,689 with 500W solar bundle. (Deal verified via coverage on 1/15/2026; confirm current price.)
EcoFlow DELTA 3 Max — flash sale price example: $749. Check the vendor listing for exact Wh; some DELTA-series models vary by capacity and configuration.
EcoFlow DELTA Pro 3 — higher-capacity pro-class units were in limited-time sales; these are large investments if you need whole-home short-term backup.

Compute cost-per-Wh using conservative usable fraction (0.80). For the Jackery 3600 example at $1,219:

Usable Wh = 3,600 × 0.80 = 2,880 Wh → $/usable-Wh = $1,219 ÷ 2,880 ≈ $0.42/Wh.

For the EcoFlow example, if the DELTA 3 Max is ~2,000 Wh (check exact spec): usable Wh = 2,000 × 0.80 = 1,600 Wh → $/usable-Wh = $749 ÷ 1,600 ≈ $0.47/Wh.

These numbers show the Jackery example gives more usable capacity per dollar in this hypothetical comparison — but double-check surge ratings, inverter output, warranty terms and whether the vendor is an authorized seller before buying.

Step 6 — Check warranty, returns and authenticity (don’t skip this)

Deals often come with limited-time price cuts through third parties. Before you click BUY, verify:

Authorized seller status (manufacturers publish authorized reseller lists)
Warranty length and coverage rider — many LFP packs have 5–10 year cycle expectations; manufacturer warranty terms vary in 2026
Return window and who pays return shipping on DOA/defective units
Availability of extended warranties or in-country service centers
Battery replacement policy — some vendors offer battery modules or service plans

Recent trend (late 2025 → 2026): more manufacturers include easy online warranty registration and longer cycle warranties for LFP models, but coverage specifics differ. Always keep purchase receipts and serial numbers for claims.

Step 7 — Advanced sizing tips and future-proofing (2026 trends)

With grid-interactive features and smart app updates common in 2026, think beyond raw Wh:

Expandable systems: Some stations (and ecosystems like EcoFlow’s) allow expansion via extra battery modules. Buying a base unit on sale and planning an add-on later can be cost-effective.
LFP vs NMC chemistry: LFP is safer and lasts longer. If you plan heavy daily usage, prioritize LFP even if up-front $/Wh is slightly higher.
Bidirectional inverter and home-wiring integration: If you want partial critical-load panel integration, confirm the station supports transfer switches or generator input wiring from an electrician.
Solar integration: Bundles (like the Jackery solar bundle) can extend runtime for prolonged outages; check charge rates and MPPT inputs.
Smart-grid updates: Manufacturers now push firmware updates for power scheduling and efficiency. Confirm over-the-air update policy and whether updates are mandatory for safety.

Three concrete buyer scenarios — pick a model type

Budget-savvy essentials (Profile A)

If you only need essentials for 8–12 hours, a 3,000–4,500 Wh nominal station will cover you. A discounted 3,600 Wh unit (like the Jackery HomePower 3600 Plus example) often fits here — check surge rating to handle your fridge. Price-per-usable-Wh matters; if the deal drops the price below $0.45/usable-Wh, it’s competitively priced in early 2026 market conditions.

Mid-range: multi-device, overnight backup (Profile B)

For 8–24 hours on multiple devices in a small apartment, aim for 2,000–4,000 usable Wh, plus a 1,200–2,500W continuous inverter to handle surges. Flash-priced mid-range DELTA-series models can be budget-friendly if their continuous/surge ratings match your needs.

Whole-house partial backup or long outages (Profile C)

If you need multiple cycles or whole-house critical loads, consider higher-capacity expandable systems (4,000–10,000+ Wh) or a modular system with external battery packs. These often aren’t cheap, but manufacturer sales in early 2026 on pro-class units (e.g., DELTA Pro 3 promotions) can lower entry cost. Verify home-install compatibility and professional installation needs.

Safety & shopping checklist (quick actionable takeaways)

Calculate continuous watts and the worst-case surge. Don’t guess — measure where possible.
Decide desired runtime and use the runtime formula to compute required Wh.
Factor in a conservative usable fraction (0.80) and inverter efficiency (≈0.88) unless manufacturer lists usable Wh.
Compare effective $/usable-Wh, not just sticker price.
Confirm surge and continuous outputs meet your peak needs.
Verify seller authenticity, warranty length, return policy, and local service centers.
For pumps/heaters or medical devices, consult an electrician or manufacturer for safe integration and load sequencing.

Tip: If a “deal” looks too good to be true on a third-party marketplace, pause. Scams and grey-market units increase after big sale cycles. Stick with authorized retailers or manufacturer storefronts when warranty coverage is critical.

Final checklist before you buy (5-minute pre-purchase walk-through)

Re-run the math with your exact device watts and target runtime.
Confirm advertised Wh and whether it’s nominal or usable. If only nominal is listed, apply a conservative usable fraction.
Check continuous & peak (surge) inverter specs versus your highest single-start device.
Read the warranty and return policy; save invoice and serial number after purchase.
Check for firmware updates and manufacturer support channels.

2026 buying strategy — how to use deals to your advantage

Late-2025 promotions created a crowded market in early 2026. Use this advantage:

Buy slightly above your minimum need if the $/Wh is significantly better — it reduces risk and improves lifecycle cost.
Prioritize verified seller discounts and manufacturer bundles that include solar or additional warranty coverage.
If locked into a long-term plan (e.g., full off-grid or frequent outages), invest in LFP and expansion-capable systems even if the initial price is higher.

Closing — take action with confidence

Do the math, protect your purchase, and use verified deals to maximize value. A correctly sized power station provides real peace-of-mind in an outage, but a mis-sized unit wastes money and can fail when you need it. Use the formulas and checklists above, verify surge & continuous ratings, and compare effective $/usable-Wh across current promotions (like the Jackery HomePower 3600 Plus and EcoFlow DELTA models noted in early-2026 coverage) before you buy.

Call to action: Ready to size your backup? Start by creating your device list and runtime target, then compare live deals from authorized retailers. If you want a quick custom calculation for your home — paste your device list and target hours below and we’ll walk through the math with recommended models and deal links tailored to your needs.

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