Franklin WH aPower Plus vs SimpliPhi PHI 3.8
The Franklin WH aPower Plus wins this battery comparison by a decisive margin. It delivers 15 kWh of usable storage with 10 kW continuous output and a 6,000-cycle rating, backed by a longer 15-year warranty. The 11.2 kWh capacity advantage provides 15 additional hours of essential-load backup.
Key Differences
- • Franklin WH aPower Plus provides 15 kWh vs 3.8 kWh usable capacity.
- • SimpliPhi PHI 3.8 achieves 98% round-trip efficiency vs 90%.
- • Franklin WH aPower Plus offers a longer 15-year warranty vs 10 years.
- • SimpliPhi PHI 3.8 is rated for 10,000 cycles vs 6,000.
Specifications Breakdown
Usable Storage Capacity
The Franklin WH aPower Plus provides 15 kWh of usable capacity (15 kWh total, 100% DoD), while the SimpliPhi PHI 3.8 offers 3.8 kWh usable (3.8 kWh total, 100% DoD). At an average essential-load consumption rate of 750 watts, the Franklin WH aPower Plus provides approximately 20.0 hours of backup versus 5.1 hours for the SimpliPhi PHI 3.8. The Franklin WH aPower Plus's 11.2 kWh capacity advantage translates to roughly 15 additional hours of essential-load backup during a grid outage. The Franklin WH aPower Plus is scalable up to 15 units (225 kWh total), while the SimpliPhi PHI 3.8 scales up to 8 units (30 kWh total).
Power Output
The Franklin WH aPower Plus delivers 10 kW continuous and 15 kW peak power, while the SimpliPhi PHI 3.8 provides 3.8 kW continuous and 3.8 kW peak. The Franklin WH aPower Plus's higher continuous output means it can simultaneously power more demanding appliances during an outage. A central air conditioner typically draws 3-5 kW, a refrigerator 0.1-0.2 kW, and an EV Level 2 charger 7-11 kW. Peak power rating matters for motor-driven loads with high startup current, such as air conditioners, well pumps, and sump pumps. The Franklin WH aPower Plus's 15 kW peak is capable of starting most residential HVAC systems.
Battery Chemistry & Cycle Life
The Franklin WH aPower Plus uses LFP chemistry with a rated cycle life of 6,000 cycles (approximately 16.4 years of daily cycling), while the SimpliPhi PHI 3.8 uses LFP with 10,000 cycles (approximately 27.4 years). Both use LFP chemistry, which is considered the gold standard for residential energy storage due to its inherent safety, long cycle life, and environmental friendliness. The SimpliPhi PHI 3.8's additional 4,000 cycles translates to approximately 11.0 more years of daily use before reaching the rated end of life.
Round-Trip Efficiency
The Franklin WH aPower Plus achieves 90% round-trip efficiency versus 98% for the SimpliPhi PHI 3.8. This means for every 10 kWh of solar energy stored in the SimpliPhi PHI 3.8, 9.8 kWh is recoverable, compared to 9.0 kWh for the other. Over 10 years of daily cycling with 15 kWh average daily throughput, the more efficient battery saves approximately $657 in energy that would otherwise be lost as heat (at $0.15/kWh average retail rate). Higher round-trip efficiency is especially valuable in time-of-use rate environments where you are storing cheap off-peak energy for expensive peak-hour consumption.
Warranty & Long-Term Protection
The Franklin WH aPower Plus carries a 15-year warranty, while the SimpliPhi PHI 3.8 offers 10 years. The Franklin WH aPower Plus provides 5 additional years of manufacturer protection against capacity degradation and defects. Battery warranties typically guarantee the unit will retain 60-70% of original capacity by end of warranty, so the length of coverage directly impacts your financial risk over the system's lifetime.
Specification Comparison
| Specification | Franklin WH aPower Plus | SimpliPhi PHI 3.8 |
|---|---|---|
| Capacity | 15 kWh | 3.8 kWh |
| Usable Capacity | 15 kWh | 3.8 kWh |
| Power Output | 10 kW | 3.8 kW |
| Chemistry | LFP (Lithium Iron Phosphate) | LFP (Lithium Iron Phosphate) |
| Efficiency | 90% | 98% |
| Cycle Life | 6,000 | 10,000 |
| Weight | 136 kg | 36 kg |
| Warranty | 15 years | 10 years |
| Scalable | Yes | Yes |
5-Dimension Head-to-Head Analysis
1. Storage Capacity
Winner: Franklin WH aPower PlusThe Franklin WH aPower Plus provides 15 kWh versus 3.8 kWh — 11.2 kWh more usable storage. At typical essential-load consumption of 0.75 kW, this equals approximately 15 additional hours of backup power. This is a substantial capacity gap.
2. Power Output
Winner: Franklin WH aPower PlusThe Franklin WH aPower Plus delivers 10 kW continuous versus 3.8 kW. This is enough to run a central AC unit, refrigerator, and general household loads simultaneously. The 6.2 kW power gap significantly impacts what appliances you can run during outages.
3. Chemistry & Longevity
Winner: SimpliPhi PHI 3.8Both use LFP chemistry with Franklin WH aPower Plus at 6,000 cycles vs SimpliPhi PHI 3.8 at 10,000 cycles. LFP chemistry provides excellent thermal stability, long cycle life, and no cobalt dependency.
4. Round-Trip Efficiency
Winner: SimpliPhi PHI 3.8The SimpliPhi PHI 3.8 achieves 98% round-trip efficiency versus 90%. Over 10 years of daily cycling with 15 kWh throughput per day, the more efficient battery saves approximately 657 dollars in energy that would otherwise be lost as heat (at $0.15/kWh). This efficiency gap is significant and meaningfully impacts lifetime economics.
5. Warranty Coverage
Winner: Franklin WH aPower PlusThe Franklin WH aPower Plus offers a 15-year warranty versus 10 years. This is among the longest battery warranties in the residential market.
Franklin WH aPower Plus
The Franklin WH aPower Plus is the enhanced version of the aPower battery, featuring 15 kWh of LFP storage with a significant power upgrade to 10 kW continuous and 15 kW peak output. It supports both AC-coupled and DC-coupled configurations, meaning it can be installed with new solar arrays using direct DC connection or retrofitted onto existing systems in AC-coupled mode. The aPower Plus maintains the same exceptional scalability as the original aPower, supporting up to 15 units for 225 kWh of total capacity. It features improved round-trip efficiency at 90%, a 15-year warranty, and works with the Franklin aGate for intelligent energy management.
Pros
- + AC/DC-coupled flexibility supports both new installs and retrofits
- + 15 kWh capacity with 10 kW continuous and 15 kW peak power is a major upgrade over the aPower
- + Same exceptional 15-unit scalability up to 225 kWh total
- + 15-year warranty with LFP chemistry for long-term reliability
Cons
- - Still requires aGate gateway for full system management
- - Relatively new product with less field history than the original aPower
SimpliPhi PHI 3.8
The SimpliPhi PHI 3.8 is a 3.8 kWh LFP battery module designed for residential and off-grid energy storage. It features 100% depth of discharge, 10,000-cycle longevity, a wide operating temperature range (-20°C to 60°C), IP65-rated enclosure for indoor or outdoor installation, and no active cooling or ventilation requirements. The 48V architecture is compatible with most off-grid and hybrid inverters including Sol-Ark, Schneider XW+, Victron, and Outback. Up to 8 units can be paralleled for 30.4 kWh total capacity. Acquired by Briggs & Stratton Energy Solutions in 2021, SimpliPhi pioneered safe, non-toxic LFP residential storage in the US market.
Pros
- + 10,000-cycle rating — among the highest in residential batteries
- + 100% depth of discharge with no capacity penalty
- + IP65 rated for direct outdoor installation without enclosure
- + -20°C to 60°C operating range — widest in the industry
- + No active cooling, ventilation, or thermal management required
- + Non-toxic, non-flammable LFP chemistry — safest battery chemistry available
Cons
- - 3.8 kWh per module requires multiple units for whole-home backup
- - No integrated inverter — requires separate inverter purchase
- - Higher per-kWh cost than newer competitors
- - 48V low-voltage system limits compatible inverter options vs high-voltage alternatives
- - Briggs & Stratton acquisition creates brand uncertainty
Choose Franklin WH aPower Plus If...
- ✓ You need more backup storage to cover overnight consumption or extended outages
- ✓ You need to power demanding appliances (AC, EV charger) simultaneously during outages
- ✓ A 15-year warranty gives you the confidence you need
- ✓ You want the flexibility to expand storage capacity over time (up to 15 units)
- ✓ Homeowners wanting maximum flexibility with both AC and DC coupling options in a highly scalable battery system
Choose SimpliPhi PHI 3.8 If...
- ✓ Maximum battery longevity (10,000 cycles) is your top priority
- ✓ You want to minimize energy losses during daily charge/discharge cycling
- ✓ Off-grid homeowners, safety-conscious buyers, and extreme climate installations needing the most durable and environmentally resilient LFP battery with industry-leading cycle life.
Our Recommendation
The Franklin WH aPower Plus is the decisive winner in this battery comparison, outperforming the SimpliPhi PHI 3.8 in 3 of 5 dimensions. Unless you have a specific requirement that the SimpliPhi PHI 3.8 uniquely addresses, the Franklin WH aPower Plus is the stronger choice for virtually every installation scenario.
Frequently Asked Questions
Which is better, Franklin WH aPower Plus or SimpliPhi PHI 3.8?
The Franklin WH aPower Plus wins this battery comparison by a decisive margin. It delivers 15 kWh of usable storage with 10 kW continuous output and a 6,000-cycle rating, backed by a longer 15-year warranty. The 11.2 kWh capacity advantage provides 15 additional hours of essential-load backup.
Which battery lasts longer?
The Franklin WH aPower Plus is rated for 6,000 cycles versus 10,000 for the SimpliPhi PHI 3.8. SimpliPhi PHI 3.8 lasts approximately 11 more years of daily cycling. LFP chemistry generally outlasts NMC in cycle life testing.
Which battery provides more backup power?
The Franklin WH aPower Plus provides 10 kW continuous (15 kW peak) versus 3.8 kW continuous (3.8 kW peak) for the SimpliPhi PHI 3.8. Franklin WH aPower Plus can run more appliances simultaneously during an outage. A central AC typically needs 3-5 kW, a refrigerator 0.2 kW, and an EV charger 7-11 kW.
Can I expand Franklin WH aPower Plus or SimpliPhi PHI 3.8 storage later?
Franklin WH aPower Plus: Yes, up to 15 units for 225 kWh total. SimpliPhi PHI 3.8: Yes, up to 8 units for 30 kWh total. Franklin WH aPower Plus offers more expansion potential.
Which battery chemistry is safer?
Both use LFP (Lithium Iron Phosphate) chemistry, which is the safest lithium battery chemistry for residential use. LFP does not undergo thermal runaway, uses no cobalt, and is inherently stable.
Related Resources
Last updated: February 2026