Published on October 21, 2026
A hybrid inverter and a battery work as one system only when the two can talk to each other. Matching voltage is not enough. Over closed-loop communication, the battery tells the inverter how fast it can safely charge and discharge, which is why inverter makers publish lists of the batteries they have tested.
This guide compares four 48V hybrid inverters and four 16 kWh LiFePO4 batteries that NAZ Solar Electric stocks. It puts the inverter and battery specs side by side, then shows which inverter and battery pairs each manufacturer documents, so you can narrow the list before you buy.
Compare the hybrid inverters
All four are split-phase 120/240V hybrid inverters for 48V battery banks, each with three MPPT inputs. The biggest practical difference is how much power each one delivers when the grid is down and the sun isn’t up. To compare other inverter types, see the inverters buying guide, or shop all-in-one hybrid inverters.
| Spec | Solis 16kW | Sol-Ark 18K | Sol-Ark 15K | Fortress Envy Duo 21 |
|---|---|---|---|---|
| Continuous AC output (grid-tied or with PV)¹ | 16 kW | 18 kW | 15 kW | 16 kW at 240V |
| Continuous output on battery only¹ | 16 kW | 18 kW | 12 kW | 12 kW |
| Surge | 2× rated for 10 s | 36 kW for 10 s | 24 kVA for 10 s (off-grid) | 2× rated for 0.5 s |
| Max PV input power | 25.6 kW | 28.8 kW usable (32.4 kW supported) | 19.5 kW | 21 kW (25 kW array) |
| MPPTs | 3 (2 strings each) | 3 (2 strings each) | 3 (2 strings each) | 3 (2, 2, and 1 strings) |
| Battery voltage range | 40–60 V | 41–63 V | 43–63 V | 40–60 V |
| Max battery charge/discharge current | 290 A | 350 A | 275 A | 250 A |
| Enclosure | Type 4X | IP65 / NEMA 3R | IP65 / NEMA 3R | NEMA 4X / IP66 |
| Weight | 145 lb | 137 lb | 135 lb | 126 lb |
| Standard warranty | 10 years | 10 years | 10 years | 10 years |
¹ The Solis 16kW and Sol-Ark 18K are rated for full continuous output on battery alone. The Sol-Ark 15K and Envy Duo 21 reach their higher rating only while solar is producing; without PV, they deliver the battery-only figure. The Envy Duo 21’s “21” refers to its 21 kW maximum PV input, not its AC output.
Read the battery-only row first
Outages often happen at night or in bad weather. Size your backup around the continuous output on battery only, then check the surge figure against the starting load of your largest motor, such as a well pump or air conditioner.
Compare the 16 kWh batteries
All four batteries use 314 Ah LiFePO4 cells at 51.2V nominal, so they store about the same energy per unit. The differences are in current limits, cold-weather heating, enclosure rating, and how far each one expands. For brand-specific detail, see the Discover HELIOS buying guide and the Renon residential battery buying guide, or shop lithium batteries.
The Fortress eBoost requires an eWay or eWay Lite wireway, sold separately.
| Spec | Discover HELIOS | Fortress eBoost | PYTES V16 | Renon Xcellent Plus Heated |
|---|---|---|---|---|
| Energy² | 16 kWh usable | 16 kWh usable (16.08 kWh nominal) | 16 kWh nominal | 16 kWh nominal |
| Nominal voltage | 51.2 V | 51.2 V | 51.2 V | 51.2 V |
| Rated capacity | 314 Ah | 314 Ah | 314 Ah | 314 Ah |
| Max continuous current | 200 A charge / 200 A discharge | 180 A charge / 250 A discharge (closed loop) | 200 A (125 A charge / 150 A discharge recommended) | 190 A |
| Built-in heating | Yes, 250 W heater, self-heats from −13°F to 46°F (−25°C to 8°C) | Yes (specs not published) | Yes, 500 W heater, 0°F to 41°F (−18°C to 5°C) | Yes, 300 W heater, activates at 41°F (5°C) |
| Enclosure | IP65, outdoor | IP65, outdoor | IP66, indoor or outdoor | IP65, indoor or outdoor |
| Mounting | Wall or floor | Floor or wall | Wall, or floor with separate base | Wall or floor |
| Max units in parallel | 36 | 16 | 16 | 31 |
| Weight | 299 lb | 309 lb (battery only) | 288 lb | 337 lb |
| Warranty | 10 years / 93 MWh throughput | 10 years; 15 with a Fortress inverter | 10 years or 8,000 cycles | 10 years |
| Safety listings | UL 1973, UL 9540, UL 9540A | UL 1973, UL 9540 | UL 1973, UL 9540, UL 9540A | UL 1973, UL 9540, UL 9540A |
² Usable and nominal energy are not interchangeable. Discover and Fortress publish a usable figure; PYTES and Renon publish nominal energy only. Usable energy also depends on your inverter’s charge and discharge settings.
Match battery current to inverter current
An inverter can only deliver its full battery-side output if the battery bank can supply that much current. Divide the inverter’s maximum battery current by one battery’s continuous rating to see how many batteries the inverter needs to run at full output. For example, the Sol-Ark 15K draws up to 275 A, and one HELIOS supplies 200 A, so full output needs two batteries.
Before you buy: which pairs are listed
Each inverter maker publishes its own list of tested batteries. The table below marks pairings named in a current manufacturer document. A pairing marked “Not listed” hasn’t been tested by that inverter maker, and each brand handles unlisted batteries differently, as explained below the table. To learn why the communication link matters, read BMS Theory: Closed-Loop Communications.
| Inverter | Discover HELIOS | Fortress eBoost | PYTES V16 | Renon Xcellent Plus Heated |
|---|---|---|---|---|
| Solis 16kW | ✓ Listed | Not listed | ✓ Listed | ✓ Listed |
| Sol-Ark 18K | ✓ Listed | Not listed | ✓ Listed | ✓ Listed |
| Sol-Ark 15K | ✓ Listed | Not listed | ✓ Listed | ✓ Listed |
| Fortress Envy Duo 21 | Not listed | ✓ Listed | Not listed | Not listed |
Sources: Solis US battery matching pamphlet; Sol-Ark Low Voltage Battery Integration Guide TB-00012 Rev. 7; Discover HELIOS integration packages 885-0131 (Sol-Ark 12K, 15K, 18K) and 885-0135 (Solis 9.6K–16K); Renon Xcellent Plus-US user manual; Fortress eBoost datasheet V.EBOOST_082025 and Envy Duo 21 datasheet V.ENVYDUO21_082025 (Fortress batteries only). Lists change; confirm against the current revision before you order.
Each inverter maker sets its own battery rules
Solis requires a battery from its approved list. Closed-loop data from an untested battery hasn’t been verified, and wrong data can tell the inverter to charge or discharge the battery improperly.
Sol-Ark inverters can run a lithium battery in open loop, but Sol-Ark prefers closed loop with a listed battery, and its warranty excludes damage caused by a battery that isn’t on its list.
Fortress builds a closed system. The Envy Duo 21 works only with Fortress batteries, and none of the other three inverter makers list the eBoost, so plan on Fortress for both or neither.
How to choose a hybrid inverter and battery pair
Define your backup loads
List the circuits you need during an outage and their combined running and starting watts. Compare that to the battery-only output row, not the headline rating. The load calculator can help you total them.
Confirm the pairing
Pick a battery that is listed for your inverter in the pairing table, and check the communication cable or kit the integration document calls for.
Size for runtime and current
Divide your daily backup energy by the battery’s usable kWh to estimate how many units you need, then make sure the count also meets the inverter’s current draw. The backup power buying guide walks through runtime sizing.
Keep reading
BMS Theory: Closed-Loop Communications
BMS Theory: Low-Temperature Charging & Battery Heating
Backup Power Buying Guide
Inverters Buying Guide
Not sure which pair fits your system?
Tell us what you want to power. NAZ Solar Electric’s solar application engineers can confirm compatibility, size the battery bank, and put together a complete system.
Frequently asked questions
Can I use any 48V battery with any hybrid inverter?
Not always. A matching voltage lets the battery connect, but closed-loop communication is what lets the inverter follow the battery’s charge and discharge limits, and inverter makers verify that link only for batteries they have tested. Rules differ by brand: Solis requires a battery from its approved list, Sol-Ark allows open-loop lithium batteries but excludes damage from unlisted batteries from its warranty, and the Fortress Envy Duo 21 works only with Fortress batteries. Check the current list before you buy.
What is the best inverter and battery combination for a home?
There isn’t one combination that fits every home. Start with the loads you need to run during an outage and compare them to each inverter’s output on battery alone. Then choose a battery that the inverter manufacturer lists as compatible, and add enough units to cover both your runtime and the inverter’s maximum battery current.
How many batteries do I need for a hybrid inverter?
Two limits set the minimum. Energy sets runtime: divide the energy you need during an outage by one battery’s usable kWh. Current sets output: divide the inverter’s maximum battery current by one battery’s continuous current rating. Use whichever number is larger.
Does a hybrid inverter deliver its full rating on battery alone?
Not always. Some inverters reach their headline rating only while solar is producing, and deliver less when the grid is down and there’s no sun. Of the four in this guide, the Solis 16kW and Sol-Ark 18K are rated for full output on battery alone. The Sol-Ark 15K drops from 15 kW to 12 kW, and the Envy Duo 21 delivers 12 kW on battery.
Do I need a battery with built-in heating?
LiFePO4 batteries can’t safely charge below freezing. A built-in heater lets the battery warm its cells so charging can resume when PV, the grid, or a generator is available. If the battery will sit in an unconditioned garage, shed, or outdoors in a cold climate, heating matters. All four batteries in this guide include it.
Manufacturer documents
Solis S6-EH2P(9.6-16)K03-SV-YD-L-US datasheet
Solis US battery matching pamphlet
Solis standard limited warranty, North America
Sol-Ark 18K datasheet PS-00036 Rev. 6
Sol-Ark 15K datasheet SK150-0001-002
Sol-Ark Low Voltage Battery Integration Guide TB-00012 Rev. 7
Fortress Envy Duo 21 datasheet
Discover HELIOS datasheet
Discover HELIOS + Sol-Ark integration package
Discover HELIOS + Solis integration package
Fortress eBoost datasheet
PYTES V16 datasheet
Renon Xcellent Plus-US user manual
