Whole-home backup is a serious electrical project. But keeping the essentials alive, a refrigerator, some lights, a modem, a CPAP, maybe a furnace blower, is well within reach of a portable home battery system. The trick is honest load math and the right battery chemistry. Here is how to plan it.
Start with a critical-load audit
Before shopping, list the devices you truly need during an outage and note each one's running watts and estimated hours of use. A modem and router might draw 20 watts around the clock. A refrigerator might average 150 running watts but only actually run its compressor a third of the time. Multiply watts by hours to get watt-hours, then sum them for a daily energy target.
This audit is the single most valuable step. It converts vague anxiety into a specific watt-hour number, which is the figure your battery capacity must meet or exceed for each day you want to run without a recharge.
- Refrigerator: ~150 running W, cycles ~1/3 of the time
- Wi-Fi modem + router: ~15-25 W continuous
- LED lighting: ~10-40 W total for a room or two
- Furnace blower: ~300-600 running W with a higher startup surge
Why LiFePO4 dominates home backup
Home backup batteries sit for months, then must deliver reliably. LiFePO4 chemistry suits this duty because it holds charge well, tolerates a wide temperature range, and offers cycle life measured in thousands rather than hundreds of cycles. Over a decade of monthly test cycles and occasional real outages, that longevity easily justifies the extra weight compared with NMC.
LiFePO4 is also more thermally stable, which matters for a large battery living in a utility room or garage. The chemistry resists thermal runaway better than energy-dense alternatives, an important safety margin for a unit you leave unattended.
Depth of discharge and usable capacity
Not every watt-hour on the label is usable. Battery management systems reserve a buffer to protect cell life. LiFePO4 systems commonly allow deep discharge, often 80 to 100 percent of rated capacity, while some chemistries recommend stopping sooner. Check the usable capacity figure, not just the nominal one, when comparing units.
Continuous and surge output for real appliances
Capacity keeps the lights on for hours; output determines whether they come on at all. A furnace blower, sump pump, or refrigerator compressor draws a startup surge well above its running watts. Your backup unit's inverter must handle both the summed continuous load and the largest single surge. If you plan to run a well pump or air conditioner, surge headroom becomes the deciding spec.
| Backup goal | Target capacity | Continuous output | Runtime (fridge + essentials) | Tier |
|---|---|---|---|---|
| Electronics only | ~500-1000 Wh | 800-1000 W | ~6-12 hrs | entry |
| Fridge + lights | ~1500-2000 Wh | 1500-1800 W | ~10-18 hrs | mid |
| Essentials + blower | ~2500-4000 Wh | 2400-3600 W | ~1 day | upper |
| Extended / expandable | ~5000+ Wh | 3600 W+ | multi-day | premium |
Compare home backup batteries
Match usable watt-hours to your critical-load audit and confirm the inverter's surge rating covers your largest motor load, such as a fridge or furnace blower.
See backup batteries →Recharging and connecting safely
Plan how the battery refills between and during outages. AC recharge from the grid is fastest when power is available; solar input keeps you running through a multi-day event. Many expandable systems accept both simultaneously, which shortens the window you spend depleted.
Powering individual appliances by plugging them into the unit is straightforward. Wiring a battery into your home's circuits through a transfer switch or subpanel is not a DIY task. Improper connection can backfeed the grid and endanger utility workers. Follow local electrical codes and hire a licensed electrician for any hardwired installation.
Consider an expandable system
Expandable units let you start with a base battery and add capacity later, so you can size to today's budget and grow toward multi-day runtime.
Shop expandable units →Extend runtime with solar
Pairing panels with your backup battery turns a fixed reserve into a rechargeable one, the difference between hours and days during a long outage.
View solar panels →From across the network
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