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How long should my batteries last with my setup?


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Hi forum fundies ....

I'm new to the game and still figuring things out.

I have an Azpert 5Kva Inverter, tied into the grid (no soloar) with 4x 12V 400W CSB Batteries (HRL 12399W) connected to give me a 48V system. My current load sits at around 15% - 18%. Its main purpose it to run my home based office during load shedding -  so its mainly computers connected. The way my inverter has been connected to the DB board has been to isolate the home office and all the lights in the house so that at night we can have some light. Only the plugs inthe office are connected. There is no geyser or aircon or fridge.

So my question ... how long (number of hours) should my system last before running our of battery power? At the moment I only get about an hour and a half which seems VERY short. Am I correct in saying so? How long should I get?

See my settings attached .. perhaps there is something I have incorrectly set.

Thanks in advance.





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I am no expert ...just have a few inverters and batteries installed.

I have a 5 kva unit with 2 banks of 48 VDC enertec premium lead acid batteries (8 batteries) ...in a factory with computers...a couple led lights ..servers ...phone system ...2 display screens ...we get around 10 - 12 hours (we have had a few long outages in Marianhill) not sure of the current load but i will be going to the factory to upload and check some info on the system 


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Those are UPS batteries that are rated at 400W/cell for 15mins. That means that their capacity is 400W*6(cells/battery)*4(batteries)/4(15minutes in 1 hour)=2460Wh.

That is the 15minute rate for those batteries. If you discharge them slower than that they will have some more capacity. But that is down to 0% or 100%DoD. They will not last very long if you discharge them that deep.

Now if you are saying that you were using 15% of the inverter capacity you were using about 750W. Lets call it 1000W to allow for losses and measurement error. You should be able to get around 2.5hours from those batteries then, but at 100%DoD. I suspect that 15-18% is not a good way to measure consumption, since you clearly did not even make 2hours.

Bottom line, no you will not be able to get 5-6 hours with your setup.

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8 hours ago, SebastianM said:

4x 12V 400W CSB Batteries (HRL 12399W) connected to give me a 48V system

How long have you had them. I am very worried that they are down to 42 volts as per your pic, that is not good for a 48 volt bank. They are either totally undercharged or they got damaged somehow. 

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I am glad to see there are people who understand this stuff... just to update ...my batteries are 105 amp/hr 12 volt enertec premium deep cycle batteries....4 batteries per bank to make up 48 VDC and i have 2 banks in parallel.

The load is 15 % and seems to last around 10-12 hours... does this sound right?


I took screen shots of the data:

output voltage - 243 V 

output apparent power - 779 VA

output active power - 576 W

load percentage - 15 % 

battery voltage 54 V

battery capacity - 100% 

battery equalization setting - enabled

equalization time - 60 min

equalization period - 20 days 

bulk charge voltage  - 58.4 V

float charge voltage - 54 V

back to grid voltage - 46 V 

Max charging current - 50 A

Max AC charging current - 20 A 

back to grid - 46 V

back to discharge - 54 V

Sebastian i hope you dont mind me sharing this thread ...it sounds like we have the same setup ...just different batteries... it would be interesting to know which are the best to use for these axpert inverters ...at a price within a budget... it would be nice to have lithium but in reality it is not going to happen anytime soon.

Battery shops are pushing lithium ...lead carbon ... gel...AGM ...dry ...and i even heard someone mention salt water batteries... i have no idea which would suit my application ...that is why i am here asking questions.







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