Deep Cycle Batteries - Help on Installation and Charging

Deep Cycle Battery - Location / installation issues:

If your deep cycle battery is to be fitted into a well ventilated area, e,g, under a bonnet or into an external battery tray then you don't necessarily need a sealed deep cycle battery, and can consider using an Access battery. Access batteries can usually be identified by the row of caps along the top which can be removed to top up the cells, although some do look "sealed" at first glance.

Access deep cycle batteries need good ventilation to avoid a build up of gasses whilst the battery is charging, however they do have the advantage of being cheaper in many cases than sealed batteries of an equivalent quality.

The ability to access the cells with a Hydrometer also makes testing easier. This can be important as the "acid test" when it comes to battery charging really is to "test the acid", and many suspected faulty deep cycle batteries are found simply to be flat or partially charged when tested with a Hydrometer. This can be due to inadequate charging or some current leakage, and obviously this needs to be fixed before replacing the battery.

The downside to deep cycle Access batteries is that the cells need regular topping up and hence they are not "maintenance-free" like their GEL or AGM sealed competitors. Also the acid can spill out of the battery if it is tipped over or inverted by mistake (or in an accident).

For Access batteries we stock and recommend a wide range. Both the USA-made Trojan batteries and Century Australia's Deep Cycle range are good value options from quality suppliers. Both of these makes come in a good range of sizes, voltages and capacities. As an aside, we have seen many Trojan & Century Deep Cycle batteries which have had a very hard life but still have good capacity left in them some five years or more after their installation.

If the deep cycle battery is going to be fitted in a poorly ventilated area, for example its going under a seat inside a caravan, then a Sealed battery which does not produce gasses while being charged is the only safe option.

Deep Cycle Batteries - Types

True Deep Cycle Sealed batteries come in 3 main construction types, which in order of increasing price (quality and all other things being equal) are as follows;

Sealed Lead Acid (SLA).

Sometimes called Valve Regulated Lead Acid (VRLA) because they contain a pressure valve which acts as a safety device to vent the battery under fault conditions (severe overcharging or internal faults).

Sealed Lead Acid deep cycle batteries work well and are fully sealed so can be used safely inside Motorhomes / Boat cabins etc. Often also used as a reasonably priced option for Golf carts (although they can often perform poorly in that application - Gel batteries are a better solution).

Overall performance is very similar to the non-sealed (wet) Lead Acid batteries, and in particular note that they are charge rate-limited and will only accept current from a charger at a modest rate, regardless of the output of the charger. This contrasts with many AGM / GEL batteries, as discussed below.

Absorbed Glass Mat (AGM).

AGM Deep Cycle batteries provide much better performance than traditional Lead Acid batteries, with lower internal resistance allowing for much faster charging and better performance under heavy load conditions.

The electrolyte is wicked up into a glass matt internally so it can never spill which is also an advantage. AGM batteries are also better in extreme cold conditions than other Deep Cycle types. Feedback from the batteries sent on the 2009 Mawson's huts expedition to Antarctica (which were Ultimate UL120 AGM batteries) was particularly good, although generally in Australia extreme cold is not a major consideration. We stock and strongly recommend the USA-made Ultimate Deep Cycle range, as well as the Ritar range.

We also stock the USA-made Optima range of spiral wound AGM batteries which are incredibly tough due to their plates being tightly wound around a circular core. Many Optima batteries have Deep Cycling or Dual (starting and Cycling) capabilities. Although they tend to have a lower Amp-Hour rating for a given size than the more traditional constructions we would still recommend them wherever vibration is likely to be an issue (such as many 4WD destinations in Australia) and for high performance applications - especially under vehicle bonnets where they can cope with the heat better than many other sealed AGM types because of their case construction.

We would strongly recommend these AGM deep cycle battery brands both from personal experience and due to good experience over the years with these makes in demanding applications without significant failures. Please contact us for more information & pricing on the AGM range of Deep Cycle batteries.

Gel Batteries.

In Gel batteries the electrolyte is mixed into a paste, which gives similar advantages to AGM batteries (i.e. non-spillable and lower internal resistance leading to better performance than traditional Lead Acid).

Although you should never flatten Deep Cycle batteries (it drastically reduces their life span), if you do have a situation where regular flattening is almost unavoidable (e.g. Golf buggies with a small battery space) then a good quality Gel battery will tolerate this better than any other type of Deep Cycle battery. Note the term "good quality Gel" as many cheaper brands are poorly mixed and perform badly in Australian conditions.

The downside with Gel batteries is that they require a lower charging voltage than standard Lead Acid or AGM types (typically 14.1V at room temperature). Gel batteries also tend to be more expensive for a given capacity than other sealed types. We stock the USA made GEL-TECH range and the German Sonnenschein brands, both of which are excellent.

Charging systems.

Solar Charging

If using Solar charging then you will need a Solar Controller or Solar Regulator to avoid over-charging the battery. These are normally purchased separately from the Solar Panel, with the exception of some "fold up" or "suitcase" style solar panels which have them built-in.

We have plenty of models in stock (both Panels and Regulators) and good practical experience with fitting Solar to caravans & Motorhomes so would be happy to advise. Many panels these days come with a silicon diode built in to avoid reverse discharge of the battery via the panel, but this is NOT sufficient to protect the battery from over-charging by the panel and a regulator must be used on all panels above a few watts in power.

Note that the latest MPPT (Maximum Power Point Tracking) solar regulators can provide up to 97% efficiency, which is a big improvement on older style regulators. This can be an advantage where space is tight and a larger panel is not an option.

Do remember to set the Solar Controller / Regulator to suit the battery type if there is an option to do so (as Gel batteries for example require a lower charging voltage, while Calcium batteries can benefit from a much higher (up to 16Volt) Equalisation charge periodically. This is something many Morningstar and other good quality regulators can provide. If in doubt please contact us for more information.


In general car or van Alternators work reasonably well with Lead Acid and AGM batteries. They are not battery chargers however and will never fully charge a Deep Cycle battery (see table above for reasons), so its best to use a battery charger when mains power is available to top up the battery charge and avoid reduced battery life from sulphation.

Note that alternator output voltages are often reduced by cable/wiring runs and Dual Battery systems so care needs to be taken to measure the actual voltage received at the battery across its terminals to ensure its adequate to charge the battery fully.

Conversely for Gel batteries fitted close to the alternator (under-bonnet with a thick gauge cabling) there is a real risk of damage due to over-charging as the alternator output can be too high for the battery.


Many Portable Generators do not have battery charging circuitry built-in and should be used with care if they provide a DC outlet (although you could plug a battery charger into the 240V socket, its a fairly inefficient way to operate unless you really need to).

The later models (from Honda etc.) with the built in chargers can provide a reasonably quick and efficient battery top-up on sites where they are allowed (or when off-site), although many users do grow tired of the noise and migrate to solar over time.

Combined charging

Finally many combinations of the above can work well. It can be difficult to fault find on systems with combined charging, although the better Solar regulators often allow the load to be isolated from the panel which can help (and assuming it has been wired up correctly - many are not).

We would be happy to advise but in general would recommend owning a good quality fully automatic battery charger to suit the batteries you are trying to maintain and using it regularly.

We stock a wide range including CTEK, Victron and Projecta to name just a few, please contact us for advice or pricing. Note that a good quality battery charger, if used regularly, will pay for itself over time through extended battery life and by operating more efficiently than the older style chargers.

Again we would be happy to provide advice on the right charger for your deep cycle battery. There is some more general advice in our Deep Cycle Help & FAQ section, or alternatively browse through our Deep Cycle Batteries online selection guide.