How long will a a 100Ah battery run a 100 watt load?
On the face of it this question is easy – I’d just create a calculator for the average 100 Ah battery discharge for all appliances that pull 50W to 1000W, but it isn’t so simple.
We use appliances in the home, so it stands to reason that the device would be a.c. at 120 volts if you live in the US, 220 volts in the EU.
You would also need an inverter, and these take some power as well.
What if the 100W was a DC load?
Then it might be be 12, 24 up to 48 volt. I’m going to assume for this article the 100Ah battery in question is 12v lead-acid deep-cycle type. (Although I prefer lihitum phosphate!)
An accurate question needs to include details of what kind of load we are connecting, if it’s going to practical:
A 100Ah 12 volt deep-cycle lead-acid battery can run a 100W continuous DC load for 6 hours if discharged to 50% as recommended. A 100Ah 12 volt lead-acid deep-cycle battery could run a 100W rated AC food-mixer for 7 hours with 50% Depth of Discharge.
Video – Battery capacity, amp-hours and watt-hours
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However, we should only discharge a lead-acid deep-cycle battery 50% of its rated capacity. Effectively, this means we can only use 50Ah, which is the same as saying 600Wh.
How long can a deep cycle battery power a fridge?
I’ll ignore inverter losses for now to make it simple. The formula is:
400W fridge running time in hours (fed from 100Ah battery) = 600 watt-hours/45W = 13.33 hours
Please note: See the chart below – note that the battery voltage reduces as the battery discharges.
This terminal voltage reduction means that when the battery is discharge to 40% to 50% of its capacity, the compressor motor inrush current may pull the voltage down so much that it triggers the inverter low-voltage alarm.
Because of this low voltage alarm issue, I would say that a more reasonable running time for a 400 watt fridge on a 100Ah battery would be 9 to 10 hours.
How do you measure amp hours in a battery?
How can you work out how much capacity is left in a 100Ah battery?
We can use the rough relationship between lead-acid terminal volts and Ah capacity to estimate remaining battery capacity.
Table – 12V Deep-cycle Lead Acid Battery Capacity Vs Terminal Volts
% State Of Charge
(12 V Lead-Acid Battery)
Battery terminal voltage
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How Long Will A 100Ah Battery Run Home Appliances – 100 watts to 1000 watts?
Use the below to find the approximate run time for RV or marine equipment running on 12V DC powered by a deep-cycle 100Ah battery.
Simply enter the wattage of the equipment and see the run time in hours:
Battery Discharge Calculator
You could also look up the load in the table below to find running time in hours:
Table: Running times for various DC and AC loads
Hours Run Time 12 volts 100Ah deep-cycle lead-acid battery (50% recommended discharge)
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