When a summer thunderstorm rolls off the Piedmont and takes a Pepco line down with it, the difference between a quiet evening and a scramble for flashlights is a battery that’s already wired in and waiting. David Williams Electric installs whole-home battery backup — Tesla Powerwall and EcoFlow — for homeowners from Bethesda to Germantown, with the panel work, transfer switch, and inspection handled by one licensed Maryland electrician (#11734) instead of a rotating crew. You get a written, up-front price before anything is touched, and a 100% satisfaction guarantee behind 30-plus years of work in these neighborhoods.
Backup that fits a Montgomery County house, not a brochure
The right battery setup depends heavily on what’s already in your basement or garage. A 1950s Silver Spring or Kensington cape often still runs a 100-amp panel with limited spare slots, while a newer Germantown or Clarksburg colonial may have a 200-amp service and room to spare. We start by reading your actual panel, your real load, and how you live in the house — then we size the system to it.
For most homes we configure backup around what matters when the grid drops: the well pump or sump in a Potomac walkout basement, the furnace and a couple of mini-splits, the refrigerator and freezer, internet and a few circuits for the home office that half this county commutes from. A single Powerwall covers essentials comfortably; two or more can carry a larger Olney or North Potomac house through a multi-day outage. EcoFlow is the flexible option when you want backup without committing to a full built-in system.
Transfer switches, panel work, and pairing with solar
A battery is only as good as the switching gear that decides what stays on when Pepco goes dark. We install the transfer equipment and, where it’s the cleaner path, a protected backup subpanel so your critical circuits cut over automatically — no extension cords run out to a portable generator in the rain. With a Powerwall and Tesla’s Gateway, the cutover is seamless; with EcoFlow we set up the transfer switch to match the loads you’ve told us you can’t lose.
If you already have rooftop solar — common on the south-facing roofs around Bethesda and Takoma Park — or you’re adding it, we wire the battery to charge from your panels so an outage doesn’t also mean watching free daytime power go to waste. Maryland’s net metering and the state’s storage incentives make solar-plus-battery a sensible pairing here, and we’ll wire it so the inspector signs off the first time.
Permits, inspection, and Pepco — handled
Battery and transfer-switch work in Montgomery County needs an electrical permit and an inspection through the Department of Permitting Services, and anything that touches your meter or service involves Pepco’s coordination. That paperwork trips up a lot of out-of-county installers. We pull the permit, schedule the DPS inspection, and handle the utility hand-off as part of the job — it’s not an add-on line item that appears later.
Because David personally holds the Maryland master license (#11734) and does the work, the inspector is looking at a clean, code-compliant install the first time around. No callbacks, no second trip, no surprise correction fees.
One electrician, a fixed price, and a guarantee
You’ll talk to the same person who quotes the job, runs the conduit, and answers the phone if a breaker trips a year later. Before any work starts you get an up-front, written price — labor, equipment, permit, and inspection spelled out — so the number at the end matches the number at the start. Every home battery install is backed by a 100% satisfaction guarantee. After three decades wiring houses across this county, David Williams Electric would rather do it right once than chase a complaint later.
Frequently Asked Questions
How long will a home battery actually run my house during a Pepco outage?
It depends on the battery size and what you're backing up. A single Tesla Powerwall (about 13.5 kWh) will typically carry a Montgomery County home's essentials — fridge, furnace, sump or well pump, internet, and lighting — through a full day or more of a normal storm outage. Pair two Powerwalls, or add solar to recharge during the day, and you can ride out the kind of multi-day outage the summer derechos and winter ice storms occasionally bring to the county. We size the system to your real loads, not a sticker number.
Do I need a permit and inspection for a battery install in Montgomery County?
Yes. Battery storage and transfer-switch work require an electrical permit and inspection through Montgomery County's Department of Permitting Services, and service-side work involves coordination with Pepco. We pull the permit, schedule the DPS inspection, and handle the utility hand-off as part of the job — it's included, not a surprise.
Can you add a battery if I already have solar panels?
Absolutely — that's one of the best setups in this area. We wire the battery to charge from your existing rooftop solar so the panels keep your battery topped up during a daytime outage, common on the south-facing roofs around Bethesda, Potomac, and Takoma Park. If you're adding solar and storage together, we coordinate both so the whole system passes inspection cleanly.
My house in Silver Spring is older with a 100-amp panel. Can it still take a battery?
Often yes, but it's exactly the kind of thing we check first. Many of the postwar homes in Silver Spring, Kensington, and older Rockville run a 100-amp service with few open breaker slots. Depending on the battery and your loads, we may install a protected backup subpanel or recommend a service upgrade. We read your actual panel before quoting so there are no mid-job surprises.
Powerwall or EcoFlow — which one is right for my home?
For a built-in whole-home solution with seamless automatic cutover, the Tesla Powerwall is the usual choice, especially when paired with solar. EcoFlow is a strong, flexible option when you want reliable backup for key circuits without a full permanent install. We'll walk your home, look at your panel and the loads you care about, and give you an honest, up-front recommendation either way.
Serving Montgomery County
David Williams Electric provides home battery installation throughout Montgomery County, including Rockville, Bethesda, Silver Spring, Gaithersburg, Germantown, Potomac, Olney. Explore all Montgomery County electrical services or learn more about home battery installation across Maryland. Call (410) 781-4357 for a free, up-front quote.
