SimpliPhi (Briggs & Stratton) Batteries

You've probably seen the Briggs & Stratton name next to something called SimpliPHI and wondered if they're related to the lawn mower engine brand. They are — Briggs & Stratton acquired SimpliPhi Power, a California battery company, in 2021. The technology didn't change, just the parent company. The SimpliPHI name still appears on the hardware.

These are not the starter batteries for small engines. This product line is for residential battery storage — pairing with solar panels, backing up your home during outages, or cutting electricity bills by storing cheap off-peak power for time-of-use savings.

All models are deep cycle lithium batteries that use Lithium Ferro Phosphate chemistry — often called LFP or LiFePO4. It's a type of lithium-ion that gives up a little energy density in exchange for much better safety and a dramatically longer lifespan. No cobalt, and far less fire risk than standard lithium-ion batteries.

Types of Briggs & Stratton batteries

Standalone batteries

Complete systems & kits

💡 The kits make sense if you don't already have an inverter — you get a pre-matched system with guaranteed compatibility.

How do the models compare?

Three models, but they're not competing for the same buyer. The PHI 3.8 does the job without extras. The AmpliPHI 3.8 adds a communications port so it can pass data to a compatible inverter — useful for more sophisticated solar setups. The SimpliPHI 6.6 is the one to buy if you're thinking bigger: more storage per unit, designed to sit outside without a cabinet, and scalable up to 18 batteries in a single system.

Key specs to pay attention to

Capacity (kWh). This is how much energy the battery stores. A typical American home uses about 30 kWh per day. One PHI 3.8 covers a few hours of essentials; three stacked SimpliPHI 6.6 units give you nearly 20 kWh — a full day of backup on critical loads.

Voltage (24V vs. 48V). Voltage must match your inverter. 48V is standard for most modern solar inverters and more efficient for larger systems. The 24V PHI 3.8 fits smaller, simpler setups.

Depth of Discharge (DoD). These batteries are rated at 80% DoD. A 3.8 kWh battery delivers about 3.0 kWh you can actually use. Don't confuse the nameplate capacity with usable capacity — they're not the same number.

Cycle life. SimpliPHI batteries are rated for 10,000 cycles at 80% DoD. Cycle daily and that's roughly 27 years of use. Most competitors max out at 2,000–6,000 cycles.

Operating temperature. The SimpliPHI 6.6 discharges down to –4°F and charges at half-rate down to 14°F — among the widest cold weather battery ranges in the industry, and no external heater required.

Round-trip efficiency. More than 90% of the energy you put in comes back out. For a solar system, that matters — less waste in the charge/discharge loop means more of your solar production actually powers your home.

BMS (Battery Management System). All models have one. It protects the cells from overcharging, deep discharge, and temperature extremes. The AmpliPHI's BMS adds a communications port for data-sharing with compatible inverters.

Which one is right for your situation?

For most people starting out, the PHI 3.8 (48V) is the practical choice. It's the most affordable model in the lineup, works with standard 48V inverters, and delivers everything you need for reliable home backup without overcomplicating things.

If your system runs on 24V — or you're powering something smaller like a cabin, RV, or off-grid setup — go with the PHI 3.8 (24V) instead. Same battery, same quality, just the right voltage for lower-draw applications.

When you need your battery and inverter to communicate — for smarter charging, real-time monitoring, or closed-loop control — the AmpliPHI 3.8 (48V) is worth the step up. The integrated BMS with CAT5 comms port handles that automatically, and the 15-year warranty makes the price difference easy to justify over time.

If you're building a larger system or want room to grow, pick the SimpliPHI 6.6 (48V). At 6.65 kWh per unit, it stores more energy in the same footprint, sits outdoors without a cabinet, and stacks up to 18 units if your needs expand down the road.

💡 No inverter yet? One of the ESS kits — Phocos or Sol-Ark — bundles a pre-matched hybrid inverter with the battery, so there's no guesswork on compatibility and setup is faster.

Briggs & Stratton LFP vs. other battery types

Lead-acid is cheap to buy and expensive to run — short cycle life, lower usable capacity, and heavier. NMC lithium is more energy-dense but contains cobalt and carries more fire risk.

LFP batteries degrade more slowly, carry less safety risk, and come with longer warranties. The 10–15 year warranty on SimpliPHI models isn't marketing — it reflects the actual lifespan you can expect from this chemistry.

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