How we calculate
The same TypeScript runs at build time and in your browser, so a page's tables and its slider can't disagree. No AI writes page copy or numbers.
Formulas
DC current
I_DC = W / (V_bus x eta), V_bus = 12 V x N_series
Worst-case current at cutoff
I_cutoff = W / (10.5 V x N_series x eta)
LiFePO4 ceiling
W_AC,safe = I_BMS x V_bus x eta
Series wiring adds volts, not amps, so I_BMS is one pack's rating. Using 12 V per block is slightly conservative against LiFePO4's 12.8 V nominal.
Peukert runtime, the starting point
t = 20 h x (C / (I x 20 h))^k
Calibrated stock curve, half to full load
t = t_half x (W_half / W)^b, b = ln(t_half / t_full) / ln(W_full / W_half)
Below half load
t = Peukert(W) x t_half / Peukert(W_half)
Raw Peukert ignores the voltage sag that trips the inverter's cutoff early at high discharge rates. We don't carry the power law below half load, because it overshoots there: about 50 min against Schneider's 31 min for the BR1500MS2 at 225 W.
Upgraded lead-acid
t_upgrade = Peukert_upgrade(W) x t_stock(W) / Peukert_stock(W)
LiFePO4
t = 60 x (cells x 12.8 V x Ah x eta x 0.90) / ((P + P_tare) x (P / P_nominal)^0.02)
LiFePO4 holds a flat plateau of about 12.8 V, so it doesn't take the lead-acid sag factor. The 90% usable energy and the tare draw of 15 W at 12 V, 22 W at 24 V and 35 W at 48 V are assumptions, not OEM figures. For comparison, Schneider's BR1500MS2 datasheet gives a tare power of 44 W, so real runtimes may be shorter at light loads. Above W_AC,safe runtime clamps to 0 min (BMS OVERCURRENT TRIP).
Lead-acid runtime is also capped at the energy its 20-hour rating holds.
Verdict
- RED: load above W_AC,safe. This beats everything else.
- GREY: load is under the ceiling, but we have no LiFePO4 pack we can show fits. Missing facts never show green.
- GREEN: under the ceiling, a single 12 V block.
- AMBER: under the ceiling, in series.
Fit check
A cell must be within 1.5 mm of the bay in each dimension. Each tab that differs from its harness clip adds one adapter to the parts list. Spade cells on a nut-and-bolt harness fail outright.
Assumptions
| Value | Used | Why |
|---|---|---|
| Inverter efficiency | 0.82 | A default, because these OEMs don't publish battery-mode efficiency |
| Half-load watts, CyberPower | rating / 2 | CyberPower doesn't state the wattage behind its half-load figure |
| LiFePO4 usable energy | 90% | Assumption |
| Inverter tare | 15 / 22 / 35 W | Assumption, at 12, 24 and 48 V |
| OR1500LCDRM2U and SMT1500RM2UC wiring | 2S2P | APC lists 24 V for SMT1500RM2UC. CyberPower publishes no bus voltage. The four-cell parallel layout is inferred, so we offer no LiFePO4 there |
| k, standard AGM | 1.18 | Engineering default, not measured per product |
| k, high-rate AGM | 1.12 | Engineering default |
| k, LiFePO4 | 1.02 | Engineering default |
| Default BMS for the calculator | 12 A | The middle of the common 10 to 15 A range. Move the slider to your pack's rating |
Series balance drift and 0 V lockout are engineering reasoning, and the charger figures are forum reports. Nothing here has been bench-tested, and no qualified electrical engineer has reviewed it.
OEM runtime benchmarks, all 35 models
The site's curve passes through both published points by construction, so those columns can't disagree. The raw Peukert columns show the error it corrects. APC figures come from Schneider's "Run time for load" calculator. CyberPower, Tripp Lite and Eaton figures come from their spec tables.
| UPS | Half load | Published | Raw Peukert | Full load | Published | Raw Peukert | b |
|---|---|---|---|---|---|---|---|
| BR1500MS2 | 450 W | 12.7 min | 12 min (-4%) | 900 W | 3.2 min | 5.4 min (+69%) | 1.99 |
| BX1500M | 450 W | 10.8 min | 12 min (+7%) | 900 W | 2.8 min | 5.1 min (+84%) | 1.95 |
| BR1500G | 433 W | 12.9 min | 12 min (-6%) | 865 W | 3.8 min | 5.4 min (+41%) | 1.76 |
| BN1500M2 | 450 W | 11.4 min | 12 min (+2%) | 900 W | 3.1 min | 5.1 min (+65%) | 1.87 |
| BE600M1 | 165 W | 11.8 min | 11 min (-3%) | 330 W | 3.2 min | 5.0 min (+58%) | 1.88 |
| BE850G2 | 225 W | 11.4 min | 12 min (+2%) | 450 W | 2.4 min | 5.1 min (+116%) | 2.26 |
| SMT1500C | 500 W | 23.1 min | 22 min (-6%) | 1000 W | 6.5 min | 9.6 min (+48%) | 1.83 |
| CP1500PFCLCD | 500 W | 10 min | 10 min (+3%) | 1000 W | 2.5 min | 4.5 min (+82%) | 2.00 |
| CP1500AVRLCD3 | 450 W | 12 min | 12 min (-3%) | 900 W | 3 min | 5.1 min (+71%) | 2.00 |
| CP1350PFCLCD | 440 W | 8 min | 8.9 min (+11%) | 880 W | 2 min | 3.9 min (+96%) | 2.00 |
| CP1000PFCLCD | 300 W | 6 min | 8.3 min (+38%) | 600 W | 2 min | 3.7 min (+83%) | 1.58 |
| EC850LCD | 255 W | 7.9 min | 7.7 min (-2%) | 510 W | 2.3 min | 3.4 min (+48%) | 1.78 |
| BR1000MS | 300 W | 12.2 min | 14 min (+14%) | 600 W | 3.7 min | 6.2 min (+68%) | 1.73 |
| BX1000M | 300 W | 10.6 min | 8.3 min (-22%) | 600 W | 2.3 min | 3.7 min (+63%) | 2.24 |
| BE425M | 128 W | 10.5 min | 11 min (+8%) | 255 W | 2.6 min | 5.0 min (+95%) | 2.03 |
| SMT1500RM2UC | 500 W | 25.9 min | 17 min (-33%) | 1000 W | 7.2 min | 7.6 min (+7%) | 1.85 |
| SMT2200C | 960 W | 28.3 min | 23 min (-19%) | 1920 W | 10.1 min | 10 min (+0%) | 1.49 |
| OR1500LCDRM2U | 450 W | 18 min | 20 min (+9%) | 900 W | 6 min | 8.7 min (+44%) | 1.58 |
| SMART1500LCD | 450 W | 13 min | 8.7 min (-33%) | 900 W | 3.5 min | 3.8 min (+9%) | 1.89 |
| 5S1500LCD | 420 W | 13 min | 13 min (-3%) | 900 W | 2 min | 5.1 min (+157%) | 2.46 |
| BR1350MS | 405 W | 11.4 min | 13 min (+16%) | 810 W | 3.3 min | 5.8 min (+78%) | 1.80 |
| BR1000G | 300 W | 13.7 min | 14 min (+2%) | 600 W | 3.5 min | 6.2 min (+77%) | 1.97 |
| BX1350M | 405 W | 10.1 min | 9.8 min (-3%) | 810 W | 2.5 min | 4.3 min (+74%) | 2.02 |
| BX850M | 255 W | 8.9 min | 10 min (+13%) | 510 W | 2 min | 4.4 min (+124%) | 2.16 |
| BN1100M2 | 300 W | 13.8 min | 14 min (+1%) | 600 W | 4.3 min | 6.2 min (+44%) | 1.69 |
| BE650G1 | 195 W | 12 min | 14 min (+15%) | 390 W | 3.3 min | 6.1 min (+83%) | 1.86 |
| CP1000AVRLCD | 300 W | 9 min | 8.3 min (-8%) | 600 W | 2 min | 3.7 min (+83%) | 2.17 |
| CP850PFCLCD | 255 W | 9 min | 10 min (+12%) | 510 W | 3 min | 4.4 min (+48%) | 1.58 |
| LX1500GU | 450 W | 14 min | 12 min (-17%) | 900 W | 2 min | 5.1 min (+157%) | 2.81 |
| CST1500SUC | 450 W | 11 min | 12 min (+6%) | 900 W | 2 min | 5.1 min (+157%) | 2.46 |
| SMC1500-2UC | 450 W | 21.4 min | 20 min (-8%) | 900 W | 6 min | 8.7 min (+44%) | 1.83 |
| SMT750RM2UC | 250 W | 16.1 min | 17 min (+8%) | 500 W | 5.5 min | 7.6 min (+40%) | 1.56 |
| OR700LCDRM1U | 200 W | 11 min | 12 min (+6%) | 400 W | 3 min | 5.1 min (+71%) | 1.87 |
| CP1500PFCRM2U | 500 W | 10.2 min | 10 min (+1%) | 1000 W | 3.1 min | 4.5 min (+46%) | 1.72 |
| 5P1500R | 600 W | 12 min | 14 min (+16%) | 1000 W | 5 min | 7.6 min (+53%) | 1.71 |
Checks on points the fit never saw
Schneider's calculator also gives 75% and 25% load. The curve wasn't fitted to these, so they test it. The other brands' curves are unchecked between and below their anchors.
| UPS | 75% load | Schneider | This site | 25% load | Schneider | This site |
|---|---|---|---|---|---|---|
| BR1500MS2 | 675 W | 6.3 min | 5.7 min (-10%) | 225 W | 31 min | 28.8 min (-7%) |
| BX1500M | 675 W | 5.5 min | 4.9 min (-10%) | 225 W | 27.4 min | 24.6 min (-10%) |
| BR1500G | 649 W | 6.8 min | 6.3 min (-7%) | 216 W | 31 min | 29.4 min (-5%) |
| BN1500M2 | 675 W | 5.8 min | 5.3 min (-9%) | 225 W | 27.9 min | 25.8 min (-8%) |
| BE600M1 | 248 W | 6 min | 5.5 min (-9%) | 83 W | 29.2 min | 26.4 min (-10%) |
| BE850G2 | 338 W | 5.3 min | 4.5 min (-14%) | 113 W | 30 min | 25.6 min (-15%) |
| SMT1500C | 750 W | 10.8 min | 11 min (+2%) | 250 W | 64 min | 52.3 min (-18%) |
| BR1000MS | 450 W | 6.5 min | 6.1 min (-8%) | 150 W | 28.3 min | 27.6 min (-2%) |
| BX1000M | 450 W | 5 min | 4.3 min (-15%) | 150 W | 27.3 min | 24.1 min (-12%) |
| BE425M | 191 W | 5.2 min | 4.6 min (-11%) | 64 W | 27.1 min | 23.7 min (-12%) |
| SMT1500RM2UC | 750 W | 12.3 min | 12.2 min (0%) | 250 W | 70 min | 58.6 min (-16%) |
| SMT2200C | 1440 W | 16 min | 15.5 min (-3%) | 480 W | 66 min | 64 min (-3%) |
| BR1350MS | 608 W | 6 min | 5.5 min (-8%) | 203 W | 26.9 min | 25.8 min (-4%) |
| BR1000G | 450 W | 6.8 min | 6.1 min (-10%) | 150 W | 35 min | 31 min (-11%) |
| BX1350M | 608 W | 5 min | 4.4 min (-11%) | 203 W | 25.1 min | 22.7 min (-9%) |
| BX850M | 383 W | 4.3 min | 3.7 min (-14%) | 128 W | 22.1 min | 20 min (-10%) |
| BN1100M2 | 450 W | 7.4 min | 7 min (-6%) | 150 W | 32 min | 31.2 min (-2%) |
| BE650G1 | 293 W | 6.2 min | 5.6 min (-8%) | 98 W | 29.9 min | 27.1 min (-10%) |
| SMC1500-2UC | 675 W | 11 min | 10.2 min (-8%) | 225 W | 52 min | 48.5 min (-7%) |
| SMT750RM2UC | 375 W | 7.5 min | 8.5 min (+14%) | 125 W | 48 min | 36.4 min (-24%) |
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