In short
- Usable energy is the capacity times the share you allow the battery to use, minus inverter losses.
- The inverter’s own consumption matters a lot at night, when the house draws little.
- Measured hours during real cuts beat any estimate, and they show you when the battery starts to age.
TAICO batteries are often bought for one reason: to keep the lights, the fridge, the fans and the internet running when the grid fails. Knowing how long they will last turns a power cut from a worry into a plan.
The four numbers
- Capacity. On the label, in kWh or in Ah. A 48 V 200 Ah pack holds about 10.24 kWh; a 24 V 200 Ah pack about 5.12 kWh.
- The usable share. From your starting charge down to the cut-off set in the inverter. Going from 95% to 15% uses 80% of the capacity.
- Inverter efficiency. Around 90 to 93% for most hybrids: part of the energy turns into heat on the way.
- The average load. What the house really draws during the cut, plus what the inverter itself uses, often 30 to 60 W.
A worked example
One 10.24 kWh pack, from 95% to a 15% cut-off, an inverter at 92% that uses 45 W for itself, and a house drawing 450 W on average:
10.24 × 0.80 × 0.92 ÷ (0.450 + 0.045) ≈ 15 hours
Double the load to 900 W with a fan and a television on, and the same battery lasts about 8 hours. Add an air conditioner and it falls to two or three. The load is the number you control.
Why the real figure differs
- The starting charge. A cut in the morning, before the sun has filled the battery, starts lower than you think.
- Peaks. A pump, a fridge compressor or an iron draws far more than the average for a moment, and the inverter losses rise with them.
- Temperature. A very hot room speeds up ageing; a cold one reduces the energy available for a while.
- Age. After a few thousand cycles, a battery holds less than it did when new. The change is slow, and easy to miss without records.
Measure it, cut after cut
The most useful figure is the one you measure: the hours the battery carried the house during each cut, and the charge left at the end. Over months, that number tells you if there is room for one more appliance, if a second pack is needed, and if the battery is ageing faster than it should.
The calculator on this site gives the estimate. TAICO Monitor gives the measured version: it reads the battery’s own state of charge and power every few seconds, keeps the history, and lets Home Assistant switch off the heavy loads when the charge gets low during a cut.
Common questions
Why does the inverter show a different percentage from the battery?
The inverter often estimates from the voltage; the battery’s BMS counts the energy in and out. The BMS figure is usually the more reliable one.
Should I set the cut-off lower to get more hours?
A little lower gives more hours tonight and a shorter life over the years. Most owners keep 10 to 20%.
Will the box run during a power cut?
Yes, if its USB charger is on the backup output of the inverter. Put your router there too to follow the battery from your phone.
