A friend in Pinelands purchased a battery with the advertised specification of 48 volts 150 a/h

The physical size is 450mm x 460mm x 190mm

The display shows

However, this is only 40mm wider than my own Shoto 5.12kWH batteries

He found that if the AC is switched off at night, with an average load of 500 watts, the battery shut down after 7 hours

Either 1 - The capacity of the battery has been over-stated, or 2 - The battery is faulty

Any ideas?

Edited September 25, 2025Sep 25 by chrisc

Some questions.

1. Is the battery shutting down or the inverter? Its a bit convenient for the battery to switch off at almost exactly 50% if we assume you continously run 500W for 7 hrs.

2. Do you know exactly how many kwh this occurs at? Any energy measurement that shows many kwh is being used.

9 hours ago, chrisc said:

Any ideas

The supplier probably quotes a 20h discharge rate at some warm temperature down to 0V timed by his grandma's favourite number.

Startup of fridges and freezers will not conform to what you expect with a constant load.

The inverter display showed 7.5 volts. I had to disconnect it, reset it and reconnect it. It took 11 hours to get it to 100%

He has 12 x 450 panels and a 10kW inverter

21 hours ago, chrisc said:

He found that if the AC is switched off at night, with an average load of 500 watts, the battery shut down after 7 hours

It's already been suggested that the inverter may be the cause of the shutdown.

My inverter will never allow the battery to be run all the way down. And there are actually two settings for this. When there is no grid it will run the battery down to 10% of capacity remaining. Then unless there is PV the system shuts down.

When there is grid it goes down only to 40% remaining then uses grid or PV.

How does it know how far the battery is discharged?

In my case (in many but not all installs) there is a comms cable between the BMS and the inverter, so the BMS is doing it's own measurements and telling the inverter about the depth of discharge.

Without that cable it relies on parameters that I have set on the inverter. If those aren't correct then the inverter may miscalculate the depth of discharge, acting like the battery is nearly exhausted when actually it still has some way to go.

The shut off percentages I mention are also configurable. I can set the inverter to not run the battery down past 40% remaining when there is no grid, or any other % I chose between 10 and 100.

Please tell us more about the inverter and the batteries: make, model, battery chemistry. And check the inverter settings.

It's some Chinese make. He bought it and asked me to install it

It does sound suspicious to me