Briggs & Stratton PHI 3.8-M 3.87kWh 48V LFP Battery
SKUPHI-3.8-48-M
The Briggs & Stratton PHI 3.8-M (model PHI-3.8-48-M) is a 48-volt lithium battery that stores electricity for later use. It holds 3.87 kWh of energy, which is roughly what it takes to run a 1,000-watt load for close to four hours using...
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Product Overview
The Briggs & Stratton PHI 3.8-M (model PHI-3.8-48-M) is a 48-volt lithium battery that stores electricity for later use. It holds 3.87 kWh of energy, which is roughly what it takes to run a 1,000-watt load for close to four hours using the full 100% depth of discharge (before inverter losses). It is a building block: you can connect more of the same 48 V batteries side by side (in parallel) to store more energy.
The battery uses lithium iron phosphate (LFP) chemistry, which contains no cobalt. Briggs & Stratton says this lowers the risk of thermal runaway (a battery overheating out of control) and fire spreading. Inside is a battery management system (BMS) that protects the cells. On the outside is a 100 A DC breaker that works as an on/off switch and as overcurrent protection (earlier production used an 80 A breaker).
The PHI 3.8-M doesn't make AC power on its own. It connects to a 48 V battery inverter or inverter/charger, and that inverter powers your home or equipment. Solar panels, the grid or a generator can recharge it through properly set-up charging equipment.
Best For
- Off-grid homes and cabins: Store daytime solar power for use at night where utility power isn't available. Briggs & Stratton lists the battery for on-grid and off-grid installations.
- Home backup: Keep critical loads running during utility outages as part of a properly designed backup system with a battery inverter.
- Replacing a lead-acid battery bank: Briggs & Stratton calls the PHI 3.8-M ideal for lead-acid battery replacement. Your inverter and charger settings must be changed to the PHI battery's settings.
- Daily cycling to cut electric bills: Rated for 10,000+ cycles at 80% depth of discharge, so it can be charged and used every day. Briggs & Stratton lists daily savings on electricity bills as a use.
- Small commercial systems: The manufacturer lists residential and commercial installations.
Key Features & Specifications
| Specification | Details |
|---|---|
| Product type | 48 V lithium iron phosphate (LFP) battery module with built-in BMS |
| Manufacturer part number | PHI-3.8-48-M |
| Nominal voltage | 51.2 VDC (a "48 V" battery). It must match a 48 V inverter or charger. |
| DC voltage range | 48–56 VDC |
| Capacity | 75 Ah |
| Rated energy | 3.87 kWh DC at 100% depth of discharge; 3.10 kWh DC at 80% depth of discharge (Briggs & Stratton's product page lists 3.8 kWh at a C/2 discharge rate). This is how much energy the battery can store. Depth of discharge (DoD) is how much of that energy you use before recharging. |
| Maximum continuous charge / discharge | 37.5 A DC (1.9 kW DC). This is the steady power one battery can deliver or accept. More batteries in parallel raise this limit. |
| Maximum discharge (10 minutes) | 80 A DC (4.1 kW DC), for short bursts of higher power |
| Built-in protection | Battery management system (BMS); accessible 100 A DC breaker on/off switch with overcurrent protection (OCPD). Earlier production used an 80 A breaker. |
| Depth of discharge | Up to 100% |
| Cycle life | 10,000+ cycles at 80% DoD. One cycle is one full charge and discharge. |
| Round-trip efficiency | 96%. About 96% of the energy you put in comes back out. |
| Charging temperature | 32°F to 120°F (0°C to 49°C). Don't charge it below freezing. |
| Operating temperature | −4°F to 140°F (−20°C to 60°C) |
| Storage temperature | 6 months: 14°F to 77°F (−10°C to 25°C); 3 months: −4°F to 113°F (−20°C to 45°C) |
| Self-discharge | Less than 1% per month |
| Certifications | UL 1973, UL 1642; certified to UL 9540; UL 9540A fire safety tested; UN 3480 (shipping class for lithium-ion batteries) |
| Terminals; battery cables | 3/8 in (10 mm) terminals. Briggs & Stratton's spec sheet lists 6 AWG as the minimum battery cable; the installation manual says each battery's leads are typically 4 AWG, sized to the built-in breaker. |
| Dimensions | 13.5 × 14 × 8 in (W × H × D); 15.5 in tall with terminals |
| Weight | 86 lb (39.0 kg) |
| Warranty | 10 years (see Briggs & Stratton's warranty document for complete terms) |
What You May Also Need
Usually required
- 48 V battery inverter or inverter/charger: Turns the battery's DC power into AC power for your loads, and usually charges the battery too. Choose one rated for a 48 V battery and sized for your loads, then program it with Briggs & Stratton's PHI battery settings.
- Battery cables: Connect the battery to the inverter and to other batteries. Briggs & Stratton lists 6 AWG as the minimum, but its installation manual says each battery's leads are typically 4 AWG, sized to the battery's built-in breaker, and local code may require sizing to the breaker or to the battery's surge rating. The terminals are 3/8 in (10 mm).
- Overcurrent protection and disconnects: The battery has its own breaker. Briggs & Stratton's manual also calls for breakers, disconnects and fuses at several points in the system so each part can be isolated and protected. Ratings come from electrical code.
May be required
- Hybrid inverter or solar charge controller: Needed if solar panels will charge the battery. A hybrid inverter combines the inverter and solar charger in one unit.
- More PHI-3.8-48-M batteries: To store more energy or deliver more continuous power. Add only more of the same 48 V model, connected in parallel.
Optional upgrades
- Battery or system monitoring: Shows state of charge and system activity. Check Briggs & Stratton documentation to confirm which monitoring products it lists for the PHI 3.8-M.
Check current manufacturer documentation before combining components, especially batteries, inverters, communications equipment and system-control hardware.
Important Considerations
- Parallel only, never series. PHI batteries are built to run at a fixed voltage. Briggs & Stratton's manual says wiring them in series to raise voltage will damage them. Don't mix this 48 V model with the 24 V PHI-3.8-24-M.
- Size the battery bank for your inverter. Briggs & Stratton's product page says battery bank-to-inverter output sizing should follow a 2:1 ratio. The installation manual explains how to size for both discharge and charge rates. Going over the battery's charge or discharge limits voids the warranty.
- Use the manufacturer's inverter settings. Inverters and charge controllers must be programmed to Briggs & Stratton's settings for the PHI battery. Wrong settings void the warranty.
- Fully charge before first use. The manual says to fully charge PHI batteries before connecting loads, and to check polarity with a voltmeter before turning on the breaker.
- Temperature. Don't charge below 32°F (0°C). Charging in sub-freezing temperatures voids the warranty.
- Location. The battery is not ignition-protected. Don't install it where ignition-protected equipment is required, such as a confined space with vented batteries, natural gas, liquid petroleum gas (LPG) or gasoline. It can be mounted terminals-up or on its side, but never upside down with the terminals facing the floor. The specification sheet doesn't list an outdoor or enclosure rating.
- Weight and installation. Each battery weighs 86 lb. Fuses, breakers and wire sizes should follow electrical code, and Briggs & Stratton recommends review by certified electricians or licensed installers.