Building a 48 V solar battery bank from 2 V cells: cell count, wiring and sizing
Twenty-four. A 48 V battery bank built from 2 V cells uses 24 cells in series, whatever their capacity: 24 × HGXL200-2 gives a 48 V 200 Ah bank, 24 × HGXL1000-2 gives a 48 V 1000 Ah bank. Every Fullriver HGXL cell, from 50 Ah to 3000 Ah, is a single 2 V nominal cell, so the count depends only on the system voltage: 6 cells for 12 V, 12 for 24 V, 24 for 48 V, 55 for 110 V and 110 for 220 V. Capacity comes from the size of cell you choose, not from how many you connect. Below: the sizing method, every HGXL size as a 48 V bank, what C1, C3, C5 and C10 mean, how the string is wired and how the charger is sized.
48 V moves the same power at a quarter of the current of 12 V, so cable, fuses and voltage drop all shrink, and it is the voltage most inverter-chargers are built around. One string of 2 V cells at 48 V is the simplest bank there is; our guide to 2 V cells versus 12 V blocks explains why.
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How many 2 V cells for each system voltage
Divide the nominal system voltage by 2 for the cell count. The table also gives the bank voltages you will see on the charger display, from Fullriver’s HGXL figures of 2.23–2.25 V per cell on float and 2.30–2.35 V per cell on cycle charge at 20–25 °C, with compensation of −3 mV per cell per °C. Bank Ah equals cell Ah, because every cell in a series string carries the same current; nominal kWh is voltage × Ah ÷ 1000.
| Tension du système | Cells in series | Float voltage (bank) | Cycle charge voltage (bank) | Temperature compensation (bank) |
|---|---|---|---|---|
| 12 V | 6 | 13.38–13.50 V | 13.80–14.10 V | −18 mV par °C |
| 24 V | 12 | 26.76–27.00 V | 27.60–28.20 V | −36 mV per °C |
| 48 V | 24 | 53.52–54.00 V | 55.20–56.40 V | −72 mV per °C |
| 110 V | 55 | 122.65–123.75 V | 126.50–129.25 V | −165 mV per °C |
| 220 V | 110 | 245.3–247.5 V | 253.0–258.5 V | −330 mV per °C |
Sizing a 48 V solar battery bank step by step
This is the method we use for customers and the arithmetic behind our calculateur de batterie de secours.
Step 1: daily energy in watt-hours
List every load the bank carries between sunset and the next useful sun, multiply watts by hours and add them up; measure refrigeration, pumps and air-conditioning rather than trusting the nameplate. Divide by the inverter’s datasheet efficiency, or as a rule of thumb add 10–15 % for inverter and cable losses, to get the daily watt-hours the bank must deliver.
Step 2: days of autonomy
Decide how many days the bank must carry the load with no useful sun. A site with a generator or grid as back-up can design for one day; a remote site with no other source usually designs for two to three. More autonomy means a larger bank that cycles more shallowly on a normal night.
Step 3: design depth of discharge
Depth of discharge (DoD) is how much of the capacity you plan to use before recharging. Any lead-acid cell gives more cycles the shallower it is worked, so the design point sits well below the deepest discharge the cell tolerates. 50 % is the usual starting point; choose 40 % where the room is hot and the bank cycles every night, 60 % where float duty dominates.
Step 4: amp-hours at the 10-hour rate
Ah required = (daily Wh × days of autonomy) ÷ (system voltage × design DoD).
Worked example: a resort villa needs 12,000 Wh a day at the battery, two days of autonomy and 50 % DoD on 48 V. Ah = (12,000 × 2) ÷ (48 × 0.5) = 1000 Ah. HGXL capacities are published at the 10-hour rate (C10), which suits solar duty because an overnight load is spread over roughly ten to fourteen hours; a load concentrated into a few heavy hours is sized against C5 or C3 instead.
Step 5: choose the HGXL model
Round up to the next HGXL size. The example lands exactly on the HGXL1000-2; a smaller villa needing 4,800 Wh with one day of autonomy comes to 200 Ah and takes the HGXL200-2. Between two sizes, take the larger: one string of bigger cells always beats two parallel strings of smaller ones.
Step 6: cell count
Twenty-four cells for 48 V, in one series string, whichever model Step 5 gave you.
Step 7: kWh, weight and footprint
Nominal energy is 48 × Ah ÷ 1000, usable energy is that × design DoD, bank weight is 24 × the cell weight, and the footprint comes from the case dimensions plus clearance. For the villa, 24 × HGXL1000-2 gives 48 kWh nominal, 24 kWh usable, 1,764 kg of cells and a two-tier rack roughly 2.1 m long and 0.5 m deep before rack steel. Now check the floor, the doorway and the room; the table below gives these figures for every size.
Every HGXL size as a 48 V bank (24 cells)
Capacities are Fullriver’s C10 ratings; usable kWh assumes 50 % design DoD; maximum charge current is 20 % of C10, Fullriver’s published limit. Footprint is the cell footprint × 24 with no gaps. The rack column assumes two tiers of 12 cells side by side on their narrow face, before gaps and rack steel; from 1600 Ah upwards the cells usually go in two rows back to back, roughly halving the length and doubling the depth shown.
| Model (× 24) | Bank Ah (C10) | kWh nominal | kWh usable at 50 % | Courant de charge maximal | Bank weight | Cell footprint × 24 | Two-tier rack, 12 per tier (L × D) |
|---|---|---|---|---|---|---|---|
| HGXL50-2 | 50 | 2.4 | 1.2 | 10 A | 77 kg | 0.19 m² | 0.59 × 0.16 m |
| HGXL100-2 | 100 | 4.8 | 2.4 | 20 A | 158 kg | 0.30 m² | 0.86 × 0.17 m |
| HGXL150-2 | 150 | 7.2 | 3.6 | 30 A | 221 kg | 0.43 m² | 1.22 × 0.18 m |
| HGXL200-2 | 200 | 9.6 | 4.8 | 40 A | 384 kg | 0.45 m² | 1.32 × 0.17 m |
| HGXL300-2 | 300 | 14.4 | 7.2 | 60 A | 542 kg | 0.62 m² | 1.80 × 0.17 m |
| HGXL400-2 | 400 | 19.2 | 9.6 | 80 A | 780 kg | 0.89 m² | 2.10 × 0.21 m |
| HGXL500-2 | 500 | 24.0 | 12.0 | 100 A | 893 kg | 0.99 m² | 2.06 × 0.24 m |
| HGXL600-2 | 600 | 28.8 | 14.4 | 120 A | 1,080 kg | 1.26 m² | 2.10 × 0.30 m |
| HGXL800-2 | 800 | 38.4 | 19.2 | 160 A | 1,476 kg | 1.73 m² | 2.10 × 0.41 m |
| HGXL1000-2 | 1000 | 48.0 | 24.0 | 200 A | 1,764 kg | 1.99 m² | 2.10 × 0.47 m |
| HGXL1600-2 | 1600 | 76.8 | 38.4 | 320 A | 2,640 kg | 3.34 m² | 4.16 × 0.40 m |
| HGXL2000-2 | 2000 | 96.0 | 48.0 | 400 A | 3,504 kg | 4.10 m² | 4.19 × 0.49 m |
| HGXL3000-2 | 3000 | 144.0 | 72.0 | 600 A | 5,280 kg | 6.02 m² | 4.24 × 0.71 m |
Cell heights over the terminals run from 166 mm to 382 mm, so a two-tier rack stands well under a metre. HGXL cells are sealed, valve-regulated and mount in any orientation, and we supply the rack drawing with the quote.
C1, C3, C5 and C10 explained
A lead-acid cell delivers less total capacity the faster it is discharged, the relationship described by Peukert’s equation, so capacity is stated at a named discharge time and Fullriver publishes four for every HGXL cell. The HGXL400-2 delivers 400 Ah at the 10-hour rate (C10), which is 40 A for ten hours; 340 Ah at C5, or 68 A for five hours; 300 Ah at C3, or 100 A for three hours; and 220 Ah at C1, which is 220 A for one hour.
This matters when you compare products. Many 12 V deep-cycle blocks are rated at the 20-hour rate (C20) and some solar batteries at C100; a slower rate always yields a higher number for the same cell, so those figures look larger than a C10 figure for identical capacity. C10 is the more conservative rating, the one used in stationary-battery sizing practice such as IEEE 485, and it sits close to a real overnight load. A 5 kW inverter flat out for three evening hours is a C3 duty; a UPS or large pump start is nearer C1. Fullriver’s figures let you size against the rate you will actually draw at.
Series wiring and inter-cell links
Connect the positive of cell 1 to the negative of cell 2, the positive of cell 2 to the negative of cell 3, and so on through all 24; the free negative on cell 1 and the free positive on cell 24 are the bank terminals. Label every cell permanently with its position, because every service visit refers to cells by number. Lay the string out as a U or serpentine so that cells 1 and 24 finish close together, keeping the two main cables short and equal and the main fuse and disconnect within reach of both ends.
Inter-cell links are short, insulated, tinned-copper bars or cables sized for the highest current the bank will pass, whether the inverter’s peak or the maximum charge current. Keep every link the same length and cross-section so each of the 46 joints has the same resistance. Terminals are M8 on every HGXL size except the HGXL100-2 (F7) and HGXL3000-2 (F10); tighten to the torque on Fullriver’s datasheet, re-check after the first month, and fit insulating covers. Place a DC fuse or breaker rated for the bank voltage close to the positive terminal, with a disconnect for service. Record every cell voltage at commissioning and after the first full cycle; that log is the baseline for the life of the bank. Keep the bank to one string: if you need more than the largest cell can give, talk to us about a higher system voltage before defaulting to parallel strings.
Charge current limit and charger sizing
Fullriver’s maximum charge current for the HGXL series is 20 % of C10: 200 A for a 24 × HGXL1000-2 bank, 80 A for HGXL400-2, 40 A for HGXL200-2. It caps the total of every source that can charge the bank at once, so add the maximum outputs of the solar controllers, inverter-charger and any generator charger and confirm the sum is at or below the limit, or set each device’s charge-current limit so the total cannot exceed it.
The limit is also a guide to how much charging to install. Returning 500 Ah to the villa’s HGXL1000-2 bank at 100 A takes about five hours of bulk charge plus absorption; at 200 A the bulk stage roughly halves. Designers work between 10 % and 20 % of C10. Set float at 2.23–2.25 V per cell (53.5–54.0 V for the bank) and cycle charge at 2.30–2.35 V per cell (55.2–56.4 V), always with a temperature sensor on the cells so the charger applies Fullriver’s −3 mV per cell per °C compensation; in a Thai battery room that one sensor does more for bank life than any other component you can fit. Our KISAE chargers take a battery temperature sensor, and the full set-up is in our guide to charging 2 V AGM cells.
Foire aux questions
How many 2 V batteries make 48 V?
Twenty-four 2 V cells in series make a 48 V nominal bank, for every capacity from 24 × HGXL50-2 (48 V 50 Ah) to 24 × HGXL3000-2 (48 V 3000 Ah). The bank floats at 53.5–54.0 V and cycle-charges at 55.2–56.4 V at 20–25 °C.
How do I calculate battery bank size for off-grid solar?
Multiply daily watt-hours at the battery by days of autonomy, then divide by system voltage and by design depth of discharge to get the amp-hours needed at the 10-hour rate; round up to the next HGXL size and use 24 cells for 48 V. For 12,000 Wh a day, two days and 50 % DoD at 48 V the answer is 1000 Ah. Our calculateur de batterie de secours does the arithmetic and shows model, cell count, kWh, weight and footprint.
What depth of discharge should I use for AGM?
Design to 50 % for a bank that cycles every night and treat the deeper discharge of an autonomy period as the exception. A deep-cycle rating is a limit, not a design target: Fullriver rates its 12 V DC series deep-cycle blocks to 80 % DoD, yet every lead-acid cell returns more cycles the shallower it is worked. A shallower design point costs capacity up front and pays it back in years of service.
What is the difference between C10, C20 and C100 capacity?
They are the same cell’s capacity measured over a 10-hour, 20-hour and 100-hour discharge. Lead-acid capacity rises as the discharge slows, so C20 is higher than C10 and C100 higher still. HGXL cells are rated at C10, the stationary-battery standard, which is conservative next to a C20 or C100 figure. Always compare capacities at the same rate.
What cable size do I need for a 48 V battery bank?
Size the main cables for the inverter’s maximum continuous current at the bank’s lowest working voltage, with a margin for surge, then check voltage drop over the actual run. A 5 kW inverter draws roughly 105 A continuous at 48 V and more at low battery voltage, so the cable is chosen from the local wiring code’s tables for that figure and upsized on long runs. We specify cables, links, fuse and disconnect with every bank we quote.
Tell us the voltage, the load and the site
Send us the system voltage, the daily load in watt-hours and where the bank will live, and we will size the string, rack, links and charging and quote with lead time. Every HGXL cell we supply is genuine Fullriver product, ordered from the factory as required and backed by stock and support in Trang; delivery covers all of Thailand, and export freight is charged at cost and invoiced separately. Contactez-nous or browse the 2 V stationary battery range.
