UPS battery backup time chart
How long a 150, 185 or 200 Ah battery lasts depends on how much you run. The first chart gives the backup from a full battery; the second gives the backup you really get each cut once daily load-shedding has drained it.
Backup from a full battery
Hours until the UPS cuts off, from a full battery, with a steady load. The load is what your appliances use together, in watts.
| Battery | 100 W | 200 W | 300 W | 500 W | 800 W | 1000 W |
|---|---|---|---|---|---|---|
| 150 Ah tubular (12 V) | 10 h | 5.6 h | 3.9 h | 2.4 h | 1.5 h | 1.2 h |
| 185 Ah tubular (12 V) | 13 h | 7 h | 4.8 h | 2.9 h | 1.8 h | 1.5 h |
| 200 Ah tubular (12 V) | 14 h | 7.5 h | 5.1 h | 3.2 h | 2 h | 1.6 h |
| 2 × 200 Ah tubular (24 V) | 28 h | 15 h | 10 h | 6.3 h | 4 h | 3.2 h |
| 2.5 kWh lithium (24 V, 100 Ah) | 16 h | 8.5 h | 5.8 h | 3.6 h | 2.2 h | 1.8 h |
| 5 kWh lithium (48 V, 100 Ah) | 31 h | 17 h | 12 h | 7.1 h | 4.5 h | 3.6 h |
Assumes the UPS uses 80% of a tubular battery and 90% of a lithium one before it cuts off, is 85% efficient and uses 20 W itself. A UPS must also be big enough for the load: a 1 kVA UPS runs up to about 800 W. Fans, lights and a router together usually use 200 to 400 W.
Real backup during daily load-shedding
With daily cuts the battery rarely starts full, because the grid is not on long enough to refill it. These are the backups per cut once the battery has settled, for a typical home running fans, lights, a router, phones and a fridge (about 405 W at night).
| Setup | From full | Light | City | Heavy | Rural |
|---|---|---|---|---|---|
| 1 kVA UPS, 150 Ah tubular | 2.9 h | 2.4 h | 47 min | 35 min | 31 min |
| 1 kVA UPS, 185 Ah tubular | 3.6 h | 3 h | 47 min | 35 min | 31 min |
| 1 kVA UPS, 200 Ah tubular | 3.9 h | 3.2 h | 47 min | 35 min | 31 min |
| 1.5 kVA UPS, 2 × 200 Ah tubular | 7.7 h | 6.7 h | 6.3 h | 1.2 h | 1 h |
| 3.6 kW hybrid inverter, 2.5 kWh lithium | 4.4 h | 3.9 h | 3.9 h | 3.9 h | 3.9 h |
Load-shedding patterns: Light: 4 h a day; City: 6 h a day, 1 h every 4 h; Heavy: 10 h a day, 2 h cuts; Rural: 16 h a day, 4 h off and 2 h on.
A bigger tubular battery on the same 1 kVA UPS gives the same backup once cuts are frequent: the UPS charger cannot refill even the smallest one between cuts. That is the recharge gap. A larger charger, solar panels or a lithium battery on a fast-charging inverter change the answer; lithium or tubular compares them.
Reading the charts: an example
A 200 Ah tubular battery running 300 W lasts about 5.1 h from full. On a 1 kVA UPS with city load-shedding of 6 h a day, the same battery gives only 47 min per cut once it has settled. How long will my UPS last? shows the calculation step by step.
Figures are from LoadReserve's calculation with typical values; see how it works.
Last updated .