How To Calculate Ah (Amp hours) and Wh (Watt hours) of a Battery Bank

For this example, I will use my own bank of stand-alone batteries and show how to calculate total amp-hours and watt-hours.

I’m not going to get into the small talk and the warnings. But it will give a quick overview to understand. Maybe one day you’ll get a glimpse of your own bank of alternative energy batteries.

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Okay, here we go…

My goal was to build a 48-volt battery (we’re talking DC) with enough watt-hours (kWh – kilowatt-hours) to power at least my main systems for a few days before I had to recharge them. I use a solar panel of about 4000 watts for charging with a charge controller followed by a DC > AC inverter system.

Why 48 volts? Because it is more efficient (than, say, 12 volts), there are fewer losses, less power, and most off-grid inverters like to chew on 48 volts….

So there are all kinds of batteries and voltage configurations. I’m not going to interfere. I’ll use 12-volt batteries in this example, because that’s what I used in this particular battery pack.

My batteries are each 12 volts and have a capacity of 100 Ah (ampere hours) each. What about the Amp Watch rankings? Simply put, we can say that this battery will deliver 1 amp for 100 hours. Or 20 amps for five hours. Did you get him?

Voltages multiplied by volts or amps gives watts. So this battery delivers 12 x 100 = 1200 watt-hours. That is 1.2 kWh (kilowatt hours) of energy.

To get to 48 volts, I put four batteries in series (connected). So this line supplies 48 x 100 = 4800 or 4.8 kWh of energy.

I have six sets of four batteries in series. Then I put these six strings in parallel. This gives 6 x 4800 = 28800 or 28.8 kWh of stored energy.

I drew a simple block diagram to illustrate my drums:

These are lead-acid batteries. Although they are more specifically AGM (absorbent) glass mats (or material), I can keep them indoors without gas.

The life of all batteries depends on the depth of discharge. The more regularly you write them, the faster they die. These parameters vary greatly depending on the specific type/chemistry of the battery, which I will not discuss here. But I just wanted you to know that.

For my particular type of battery, I avoid discharging above 30% of the upper limit (30% STR of depth of discharge). In my case, it helps a lot with battery life.

This means that I will try not to use more than 30% of the 28.8 kWh or about 9 kWh of energy for a given battery before recharging it.

This is enough to power me for a few days for my needs, such as my furnace in the winter (which is also connected to my hot water), my refrigerator, my freezers, and my well pump.

We have a lot of winter days here, so it works pretty well. I have tons of energy in the summer, so I run the whole house (including air conditioning) through the system. Although the air conditioning is off at night (electric pigs).

Okay, that was just a quick way to calculate amp and watt hours.

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Frequently Asked Questions

How do I calculate my battery hours?

Amp-hour (at 12 volts) = watt-hour / 12 volts = 1470 / 12 = 122.5 amp-hour. If you use a different battery, the amp-hour voltage changes by dividing it by the voltage of the battery you are using.

How do I calculate the battery bank in kWh?

To determine how many kWh a battery will consume, simply multiply the rated amp-hour rating (Ah) by the required system voltage. To meet the above-average kWh requirements, the best battery size would be a 225 Ah system at 12 volts with 2 batteries.

How do I calculate WH of ah?

The formula is (Ah)*(V) = (Wh). If you z. B. a battery of 2 Ah with a nominal voltage of 5 V, then its capacity is 2 Ah * 5 V = 10 Wh.

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