Choosing between a wall-mounted, stacked, rack or floor-cabinet battery is not a spec-sheet exercise — it is a site decision. Wall-mounted LiFePO4 storage is the right default for most European retrofits because it saves floor space and covers 2.56–14.34 kWh in a single unit. Choose a stacked tower when the household will grow module by module to 10.24–30+ kWh and the floor is the better place for the weight. Choose rack-mount when the battery lives in a 19" cabinet or equipment room and needs to scale toward 60 kWh for larger homes or light-commercial loads. Here is the decision framework we use with installers and distributors.
The formats, and why the difference matters
All of the formats here are built on LiFePO4 chemistry. The real difference is mechanical and electrical architecture: where the unit lives, how much weight the wall or floor carries, how far the system can grow, and which bus voltage the inverter needs. Choosing the format early avoids a re-install later.
- Wall-mounted. A slim cabinet that bolts to a structural wall with no floor footprint. Typical capacity 2.56–14.34 kWh per unit, expandable with parallel units.
- Stacked. A floor-standing tower built from 5.12 kWh modules. Two to six modules deliver 10.24–30.72 kWh, in low-voltage and high-voltage (up to 1000 VDC) bus versions.
- Rack-mount. Standard 19-inch modules for cabinets and equipment rooms. One to twelve modules scale from 5.12 kWh to about 60 kWh, which is why rack systems suit larger or light-commercial backup.
- Floor cabinet. A high-capacity single cabinet (14.34 kWh per unit on 280 Ah cells), parallel to about 57 kWh for whole-home loads.
Wall-mounted: the retrofit default
For the typical European retrofit — an existing PV array, a garage or utility room that is already full — wall-mounted storage is usually the cleanest answer. It disappears onto the wall, keeps the floor clear, and the Storage Wall series covers 2.56, 5.12, 10.24 and 14.34 kWh in one unit, with an IP65 outdoor variant for sites where the garage is not an option.
The one thing to verify before committing is the wall itself. A fully loaded wall unit is heavy and has to be anchored to a structurally sound wall — masonry or a stud wall with the correct fixing. Installers consistently list structural support, weight and loading among the first checks when comparing wall-mount with floor-standing formats (source). If the wall is plasterboard over an unbraced cavity and cannot be reinforced, that alone can push the decision to a floor-standing format.
Stacked: modular growth for the household that will expand
Stacked towers trade a little floor space for a clear growth path. Because the stacked series is built from 5.12 kWh modules, you can install two modules today and add a third or fourth when the household adds a heat pump, an EV or more PV.
The stacked series is offered in low-voltage and high-voltage (up to 1000 VDC) bus configurations, so it can match the inverter architecture the project already uses. The main site constraints are footprint and service access: the tower needs a clear floor area and room to reach the modules.
Rack-mount: the equipment-room workhorse
Rack-mount modules are designed for the electrical room, not the living room. A standard 19-inch module slots into a cabinet, and the rack series scales from a single 5.12 kWh module to about 60 kWh in a high-voltage system.
Rack is the strongest choice when the battery shares a room with the inverter and switchgear, when the site provides front-and-rear service access, and when the project is large enough to justify the cabinet. For a normal family home, a full cabinet in the utility room is usually more than the site needs — that is where wall or stacked is the better fit.
Floor cabinet: high capacity in few boxes
When the goal is whole-home backup or light-commercial loads without juggling many modules, a floor cabinet gives you 14.34 kWh in a single unit and up to about 57 kWh in a parallel bank. It suits sites where "few boxes, high capacity" matters more than modular granularity.
Six questions to match the format to the site
Run through these in order, and the format usually selects itself.
- Where will the battery physically live? A clear wall → wall-mounted. A floor area → stacked or floor cabinet. A cabinet or equipment room → rack.
- Can the wall take the weight? If the structure is uncertain and cannot be reinforced, choose a floor-standing format and remove the question.
- What does the household need today — and in three years? Static needs up to about 14 kWh → wall. Planned growth → stacked. Larger or light-commercial loads → rack.
- Which bus voltage does the inverter need? Match the system to the inverter's supported voltage range; high-voltage architectures favour stacked or rack.
- How much service access and airflow does the site allow? Rack needs cabinet access; stacked needs floor space around the tower.
- What does your own team stock and know? Standardising on one format cuts training, spares and callbacks.
Format comparison table
| Criterion | Wall-mounted | Stacked | Rack-mount | Floor cabinet |
|---|---|---|---|---|
| Typical capacity | 2.56–14.34 kWh per unit | 10.24–30.72 kWh (2–6 modules) | 5.12–60 kWh (1–12 modules) | 14.34–57 kWh (1–4 units) |
| Floor footprint | None — wall mounted | Floor tower | 19-inch cabinet | Floor cabinet |
| Wall structural load | Yes — must be anchored | No | No | No |
| Growth path | Parallel units | Add modules | Add modules | Parallel units |
| Voltage architecture | 48 / 51.2 V | Low & high (up to 1000 VDC) | High-voltage systems | 51.2 V |
| Best-fit site | Retrofit garage / utility room | Growing household, new builds | Equipment room / light-commercial | Whole-home backup, few boxes |
Don't stop at the format
The format decides where the battery lives and how it grows. The criteria that follow matter just as much: the BMS communication protocol and the verified inverter compatibility list, the cycle-life test conditions behind the datasheet, and the certification that applies to the specific SKU. Evaluate format and supplier together, not in isolation. For the next steps, see how to size the battery correctly, what site preparation an install really needs, and which inverter compatibility questions to ask before choosing a storage supplier.
Frequently asked questions
Which home battery format is best for a retrofit garage install?
Wall-mounted, in most cases. It keeps the floor clear, covers 2.56–14.34 kWh in a single unit and can be expanded with a parallel unit. Confirm the wall structure can carry the loaded weight before committing.
Can a wall-mounted battery be expanded later?
Yes. The Storage Wall series supports parallel expansion, so you can start with one capacity and add a second unit when the household load grows.
When should I choose a high-voltage stacked or rack system over a low-voltage wall unit?
When the project needs more than a single wall unit's capacity, when the inverter is designed for a high-voltage DC bus, or when the site is large enough to justify a cabinet or module tower.
Do rack batteries need a dedicated cabinet?
Rack modules are built for 19-inch cabinets with proper mounting, cable management and airflow. Installing rack modules without a suitable cabinet is not a realistic option for a finished installation.