The Ultimate Guide to Solar Batteries

When you’re out camping, fishing, hunting, or on longer off-road trips and far from a mains connection, you’ll want a dedicated secondary battery to power all your devices and appliances. Car batteries aren’t suitable for this purpose, as they offer short bursts of high power. Instead, look to deep cycle batteries that drain power in slower cycles and with just the right output. Charging these is also simpler. Most people will connect batteries to panels in a solar setup, but DC-DC or main chargers also come in handy.

Deep cycle batteries that store excess power from that produced by solar panels are often simply called ‘Solar Batteries’. They are one of the parts of dedicated off-grid systems, with things like charge controllers and monitors keeping things safe and warranting that you have enough power during the day. Choosing batteries for a solar system will depend on your power needs, the types of devices and appliances you run, and whether you’re after more efficiency and longer use.

Types of Solar Batteries

Deep cycle solar batteries differ from the starter battery in your car in the way they function, as well as in build. Starter batteries can only discharge a small portion of their capacity and at single bursts at a time. Adversely, a deep cycle battery can be discharged over longer periods and up to 50 per cent (80 in Lithium batteries) of overall capacity, meaning items hooked up to the battery can run for longer periods.

Build-wise, starter batteries have numerous lead plates that provide a larger surface area for the electrolyte to react and provide a higher output. Deep cycle solar batteries, on the other hand, have fewer and thicker plates, meaning less surface area for electrolytes. This allows for a slower discharge rate.

Different designs and chemistry in a solar power deep cycle battery lead to different types. The most common are Lead Acid, Absorbent Glass Mat (AGM) and Gelled Batteries, as well as batteries based on Lithium.

Flooded Lead Acid Batteries

These are some of the older designs, but still used today. They have lead plates that are flooded in an electrolyte mix of sulphuric acid and water. When they are charged or discharged, the chemistry changes, leading to a drop in electrolyte levels and the release of gases. Flooded Lead Acid solar batteries can be discharged up to 50 per cent of their capacity, but the need for more maintenance and careful storage makes them the cheapest type of battery for your solar system. Another thing putting them at a disadvantage is the weight, and those in larger capacities are close to 50 kilos.

Sealed batteries

You’ll find these in two flavours – Absorbent Glass Mat and Gel. AGM batteries have lead plates divided by thin layers of fibreglass which help absorb the electrolyte mixture, and as such, they’re way more efficient and require less in the way of maintenance. Safety is improved and you don’t have to think about storage.

Similar are Gel batteries. These have the same electrolyte mix, but floating in a gel silica compound. They too are easier to maintain, come in a lot lighter and have higher safe discharge and charging rates. What’s more both sealed battery types have longer life cycles, so they’ll last more. The bonuses mean a slight premium over flooded lead-acid batteries.

Lithium Batteries

With gradual price reductions, safer tech and longer use, lithium batteries are now the go-to choice for serious campers and off-roaders. They’re much lighter, can be easily handled and are virtually maintenance-free. They don’t gas or leak, so are also much safer. The main upside though is the 80-100 discharging rate without impacting battery health. Lithium batteries also charge faster and have longer life cycles meaning they’ll last for years (roughly five times more than a lead-acid battery in the same capacity).

Constant improvements, like recent LiFePo or Lithium Iron Phosphate batteries, have led to extremely long life, constant voltage (irrelevant of remaining charge), optimal heat handling and vastly lower weight. This all comes at a cost, but one worth the convenience alone.

What to Look for in Your Next Solar Battery:

• Capacity Rating – this is how much current appliances and devices can draw from the battery for a specific time. Capacity is stated in Amp-hours (Ah) and the higher the number the more capacity.
• Life Cycles – this defines the number of times a battery can be discharged and recharged without affecting performance. Lithium batteries perform best here, coming close to 5000 cycles.
• Depth of Discharge – or the level to which the battery can be safely used, before it needs to be recharged. Lead batteries fare worst, and lithium batteries perform best here. The middle ground is held by AGM and Gel batteries, and these are a decent choice for small to medium solar setups like those found in caravans and 4WDs.

Other Considerations

Price will be the main if not the first factor when buying batteries for the solar system. Lithium batteries are the most expensive and worth the extra cost if you need more juice in a larger solar setup. If running just a few things like phones or lights, even the cheapest lead-acid battery in a lower capacity will be fine. This all depends on how much power you need and for how long. More demanding loads might require a step up in voltage with a bespoke solar inverter.

To keep batteries in top condition, get an inexpensive battery monitor, which will also tell you how much power you often consume and how much power is going to the battery from the panels or chargers. You’ll find batteries and all items listed for your solar installation at well-stocked camping, 4WD and specialist solar stores throughout the country.