What your home battery does during an outage vs an ERCOT price spike — and why they're different events

Outage mode: anti-islanding and the 20-millisecond switch

At 3:14 AM during a Williamson County ice storm, Oncor's wires go quiet. PUCT Substantive Rule §25.211 — the Texas codification of IEEE 1547⁵ — requires every distributed-generation interconnection to detect grid loss and disconnect within a defined window. The Base-installed battery accomplishes it with a transfer switch, and the switch trips fast.

The systems Base ships transfer within milliseconds — fast enough that lights flicker but most household electronics keep running. The fridge keeps humming. For Plano customers with CPAP machines, home-office workstations, or medical devices, we pair the battery with a small UPS at the always-on boundary — that's part of the install spec we walk through during the home survey.

Once the transfer is open, the battery is the household's only power source. The BMS holds your customer-controlled reserve floor — set during install and adjustable later — below which the battery won't discharge to preserve cell health. On a Base 25 kWh single at a 20% reserve, that leaves about 20 kWh of usable capacity (40 kWh on the 50 kWh dual). Runtime depends entirely on what circuits Base wired through the backup panel; the sizing guide walks the math household by household.

While the grid is down, the battery does not push power back through the meter — anti-islanding is a hard requirement, not a soft preference⁵. Solar-paired systems can still produce during the outage (sunlight doesn't care about Oncor's restoration timeline) and route that production into household loads or battery recharge, but none of it goes back onto the dead wires. That's the rule that keeps line workers from being electrocuted by a homeowner's battery during restoration.

Price-spike mode: how Base's VPP dispatches when the grid is up

ERCOT issues an EEA Watch when reserves tighten — typically 30–90 minutes ahead of EEA Level 1². The grid is still up; no TDU is shedding load. But ancillary-service prices are clearing high (RRS, ECRS, regulation), and the wholesale energy market is signaling that the next few hours will need every fast-responding resource available.

For Base-enrolled batteries in Round Rock and Plano homes, this is dispatch territory. Our controller receives ERCOT signals and fans them to enrolled batteries over cellular. The battery's inverter ramps to commanded output within 500 ms¹². We may charge the battery hard from the grid for an hour ahead of the spike (so it has full capacity to dispatch), then discharge during the high-clearing hours. The customer notices essentially nothing — the state-of- charge meter ticks down a few percentage points; the fan kicks on briefly.

The grid stays up the entire time. No transfer switch opens. No anti-islanding triggers. The battery is operating as a small ERCOT-market resource for Base, not as a backup device. The revenue from the dispatch flows ERCOT → Base → priced into the customer's bundled rate (rather than landing as a separate payment customers have to track — see how our VPP works for why we structure it that way).

Your reserve floor is the safety mechanism. Even during heavy market dispatch, Base never crosses below your configured reserve threshold⁷. A Plano household running a 40% reserve never discharges below 40% state-of-charge — leaving 10 kWh of usable capacity (on a 25 kWh single) ready for the backup case the moment the grid drops. The reserve floor is what makes "the battery prioritizes your house first" a physical fact rather than a marketing claim.

Combined mode: how Base handles wires-down AND prices-spiking

Winter Storm Uri (February 2021) was a combined event¹. ERCOT wholesale prices were administratively pinned at the $9,000/MWh ceiling for nearly five days. Distribution wires were also down across Oncor, CenterPoint, and AEP service territories — 4.5 million Texans were without power, many for 36–72+ hours. Pre-HB 16 wholesale-indexed retail customers (Griddy and similar) saw five-figure bills¹; HB 16 banned that retail-product class effective September 2021⁸.

For a Base-enrolled battery riding through a Uri-class event, the operating sequence interleaves modes — and our controller is built around the sequence. As EEA conditions tighten, we switch the battery to backup-priority mode and charge hard from the grid before the wires go down². The moment your distribution feeder opens, the transfer switch isolates the battery to your critical-loads panel. With the grid dead, no VPP dispatch is possible — Base steps back, and the battery operates as pure backup for your house. As Oncor begins restoring service for some neighborhoods earlier than others, once your feeder comes back, our controller resumes VPP operation for the post-event ancillary-market windows.

The reserve-floor architecture is what makes the combined- event case workable. A Base-enrolled battery with a 60% reserve floor going into Uri's first day would have entered the outage window with 60%+ state-of-charge — closer to 100% in practice, because our EEA Watch protocol would have charged it hard immediately before the wires went down. That's 24+ hours of essentials on a 25 kWh single, or 48+ hours on a 50 kWh dual — enough to clear most Williamson and Collin county Uri-pattern restoration timelines.

Three real Texas events, three different battery responses

Winter Storm Uri — February 2021 (combined event)

Five-day cold snap; ERCOT debt securitization; 4.5 million customers without power¹; Griddy wholesale-indexed customers with five-figure bills before HB 16 banned the structure⁸. A Base-installed battery riding a Uri-class event today would: charge hard ahead of EEA Watch² under our controller's direction; enter outage mode the moment its feeder dropped; operate critical-loads-only for 24–72 hours per battery size and reserve floor; re-enter Base VPP dispatch when Oncor restored its feeder. The combined event is the binding sizing case for households worried about tail risk — and it's why Base's bundled product centers on whole-system behavior, not on backup-only equipment.

Houston derecho — May 16, 2024 (outage-only)

Severe-thunderstorm derecho event with sustained 80+ mph winds across Houston metro. CenterPoint reported ~2.2 million customers without power at peak; restoration ran 48–96 hours for the long tail³. ERCOT-wide grid prices were normal — the derecho was a pure distribution event, not a generation shortage. Base-installed batteries in CenterPoint territory operated in pure backup mode for 48–96 hours; no VPP dispatch possible because feeders were down. Households on grid-only backup (small generators, portable power stations) ran through fuel and food spoilage; Base whole-home customers with critical-loads sub-paneling cleared the median outage.

ERCOT EEA Watch — June/July 2024 (price-spike, no outage)

ERCOT issued multiple EEA Watch declarations through summer 2024 as load tightened reserves². No customer-side outages resulted; reserves held. ECRS clearing prices ran sharply above baseline during these events². Base dispatched our enrolled fleet heavily through these windows and captured premium ancillary-service revenue, which flowed through to the bundled rate our customers pay. Customer-side experience: zero interruption. The grid stayed up. The battery worked without bothering anyone in the house.

What the three modes mean for buying a battery

Three operational implications a Texas household should carry into the buying decision:

1. Transfer-switch latency matters for what you back up. The systems Base ships transfer within milliseconds — fast enough that lights flicker but most household electronics keep running. Houses with always-on critical electronics (CPAP, home-office workstation, medical devices) get a small UPS paired alongside the battery as part of the install.
2. Reserve-floor architecture is what guarantees backup priority. A VPP-enrolled battery with a customer- controlled reserve floor preserves the backup case regardless of market dispatch activity⁷. EEA Watch protocols add a second layer — automatic switch to backup-priority mode ahead of grid stress². The combination is what makes "the battery prioritizes your house first" reliable in practice, not just on a marketing page.
3. Size for the outage tail; let VPP enrollment pay for the size-up. The combined-event case (Uri-class) is what determines whether your household actually rides through the worst event your zip code has seen this decade. Sizing for that tail, then enrolling in a VPP to capture dispatch revenue⁷, makes the same battery serve both the outage and the price-spike cases without trade-off.

When the three-mode framing doesn't change anything

For a Texas household whose primary motivation is grid-price protection without any backup interest — a renter, a small-footprint single-occupant home, a household whose Round Rock or Plano neighborhood logged zero outages of any length in the last three years — the outage-mode discussion is academic. A fixed-rate plan handles the price-spike side without any battery⁸; the EEA Watch protection isn't relevant to your household if you're never going to install backup.

Conversely: a household whose only motivation is a backup device and who has zero interest in VPP enrollment can ignore the price-spike-mode discussion entirely. The battery sits at 90%+ state-of-charge most days; the only operational mode that matters is outage; sizing comes down to runtime. Both frame-collapses are valid. The three-mode framing matters most for households whose answer to "why are you buying a battery" is some mix of backup, economics, and Texas-grid-tail-risk hedging — which is, in 2026, most Texas households who buy batteries.