150 Ah flat plate battery only lasts 1.5 hours

Question

I have a 150 Ah battery with a 1000 W square wave inverter. I'm only using the inverter for a 4 ft LED tube light, a router, and a gaming laptop (Dell g5 15 5590).

I was expecting the battery to last for a good 4 to 5 hours, but the battery only lasts for 1.5 hours. Both the battery and the inverters are new. The batteries were also fully charged. On the laptop adapter, it says 180W, so I'm guessing the laptop only uses 180 W (not sure though).

Is it normal?

Answer 1

Ballpark figures, I'd expect to be able to use maybe 2/3 of the battery rated capacity, at around 12 V. So you might have around 1200 Wh.

The inverter (of unknown make and model) maybe only has an efficiency of 80 %, leaving you with around 1000 Wh usable energy.

So with a load of around 200 W, I too would expect around 4-5 hours of runtime.

There may be a few possible reasons why you see such short runtime. Including:

• Battery capacity not being as high as marketed
• Load being way higher than you think
• Battery was not actually fully charged
• Inverter cuts off early (at not so low voltage), using only a fraction of the available energy in the battery
• Inverter having terrible efficiency
• Inadequate wiring, causing voltage drop before the inverter

You could do some further testing to figure out what is going on, like loading the inverter with a known load while monitoring the battery voltage and current.