Deep cycle battery voltage & state of charge

battery levels

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Owning a mobile or off-grid solar power system means obsessing about how much charge is left in your deep cycle battery bank.

A battery bank is a set of batteries that are interconnected that store electrical energy. Other than solar power systems, a battery bank is also used in cars, RVs, and boats. The remaining amount of charge that a battery bank has is known as the “stage of charge”. You can determine the state of charge by looking at the AGM battery voltage chart or a deep cycle battery voltage chart.

Most owners are concerned about the life span of their batteries, some are worried if they have enough voltage that  meet their needs. If you own a solar power system but are unsure whether you need to get a battery, then ask the trusted experts at Energy Matters to help you get started. 

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While not totally accurate, the easiest way to determine this is with a multimeter if your solar regulator or charge controller doesn’t have a voltage readout.

The state of charge does vary a little between sealed lead acid, flooded, gel and AGM deep cycle battery types and also between brands. Even the weather can play a role.

Batteries perform better in colder weather and have a higher state of charge reading on an AGM voltage chart. In warmer conditions, the battery’s performance decreases, as well as the state of charge. To ensure that you only get the best battery state, it is crucial to keep these factors in mind.

Battery voltage state of charge chart

Battery voltage state of charge table

The battery voltage chart below shows the voltage and approximate state of charge for each type of battery, including AGM batteries, lead acid batteries, and car batteries.

Note: The figures in the AGM battery voltage chart, lead acid battery voltage chart, and car battery voltage chart are based on open circuit readings. That is when the deep cycle battery hasn’t been under load for a few hours. This scenario may not occur very often in a battery based system that’s in continual use.

So, the best time to take the reading is early in the morning before the sun hits your panels, in the evening as the sun is setting, or when it’s very overcast. If you take a reading while the battery is receiving charge, it could read anything up to 14.5 volts.

If you take the reading when the panels aren’t exposed to the sun, as there will likely be power being drawn at the time, you can assume that whatever the voltage reading, it’s a conservative estimate. Once all load is removed from a battery, the voltage can bounce back up substantially. Take a look at the chart below:

State of Charge Sealed or Flooded Lead Acid battery voltage Gel battery voltage AGM battery voltage
100% 12.70+ 12.85+ 12.80+
75% 12.40 12.65 12.60
50% 12.20 12.35 12.30
25% 12.00 12.00 12.00
0% 11.80 11.80 11.80

Energy Matters has been a leader in the renewable energy industry since 2005 and has helped over 40,000 Australian households in their journey to energy independence. 

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Battery depth of discharge

Battery depth of discharge


The general rule of thumb: the less your deep cycle battery discharges before recharge, the longer it will last.

Here’s an example:

A Sonnenschein Solar Bloc 100 AH Gel Battery discharged to a depth of 70%, i.e. with only 30% or 30 Ah (amp hours)  remaining, will have a lifespan of around 1200 cycles, which is quite impressive. 

However, if it only discharges to 50%, the expected number of cycles skyrockets to around 1700! If a cycle is a day, that adds over 1.25 years to the life of the battery.

Depth of discharge, also known as DOD, shouldn’t be any more than 50% in most deep cycle batteries in order to get the best value for money. So if you have a 100 AH battery, consider the cut-off discharge depth being 50 AH.

Measuring your Depth of discharge is a very important calculation you should make when choosing the size of a deep cycle battery.

Here’s another example:

If you want to power a laptop computer, check the amps rating on the adaptor. It’s likely to be somewhere between the 3 and 5 amp mark. This translates to probably around 2 – 4 amps an hour under normal usage as your laptop won’t be using the full amount at all times. So, based on the lower end:

100 AH battery = 50 AH available capacity/2 amp draw = 25 hours usage.


Four main types of conventional deep cycle and lead acid batteries

Four Main Types of Conventional Deep Cycle and Lead Acid Batteries


There are many lead acid batteries on the market. But there are four types that are commonly used – sealed lead acid, flooded lead acid, gel, and AGM.

The four main types have their own advantages and disadvantages. It is important to determine which type meets your budget, as well as your preferences. Let us take a closer look at deep cycle batteries and lead acid battery voltage, including AGM battery voltage.

Sealed lead acid battery

Sealed lead acid batteries are the most common type of deep cycle battery used at home. They are favored by residential and business properties as they are maintenance-free and have a long lifespan. However, they are also the heaviest type of battery.

Flooded lead acid battery

Flooded lead acid batteries require periodic maintenance and adding water to the cells, but they are less expensive than other types of batteries.

Gel batteries

Gel batteries are similar to sealed lead acid batteries in that they are maintenance-free, but they are more expensive and may not last as long. Gel battery voltage is typically around 2 volts per cell, which means a 12-volt battery delivers six cells.

AGM batteries

AGM batteries are the most expensive type of battery, but they provide the best performance and have the longest lifespan. AGM battery voltage may depend on the specific model and the manufacturer. AGM battery’s minimum voltage is 12 volts, meaning it can produce 12 volts when fully charged.

Solar charge controller

Other than lead acid batteries, you must also consider a solar charge controller. A solar charge controller is an important part of any solar power system. They regulate the flow of power from your panels to their batteries, thus, preventing them from overcharging.

One main factor when choosing a solar charger controller is the type of panel you own, battery size, and the amount of energy source you need to generate.

Choosing the right battery voltage for your needs

Choosing The Right Battery Voltage For Your Needs


Battery manufacturers aim to produce the best products in the solar industry, so it’s vital that you choose a reliable and reputable brand. With a number of factors to consider, it is no surprise that batteries can be quite confusing.

Energy Matters for your solar power needs

At Energy Matters, we pride ourselves on being the experts when it comes to solar energy in Australia. Our staff is always happy to share that with our clients. Call us today for a free solar quote!

Contact Energy Matters and get your free quote today! You may also visit our site to learn more about solar energy. Use our online quote tool to begin your solar journey today. 

To learn more about the difference between them, view our deep cycle battery guide. Find out more about solar battery and Tesla Powerwall today.

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Energy Matters for your solar power needs

At Energy Matters, we pride ourselves on being the experts when it comes to solar energy in Australia. Our staff is always happy to share that with our clients. Call us today for a free solar quote!