Deep Cycle Batteries - Flooded or Sealed

A common Deep Cycle battery question is whether to go for Flooded (or Wet lead acid) batteries or the newer Sealed (Gel or Absorbed Glass Matt (AGM)) types. Its not a simple answer but some of the pro's and cons are listed below.

If you have other questions then feel free to drop in for a chat, or call/email us. We have good parking at the Stores and we can size up & test batteries with you to suit your needs.

Flooded versus Sealed

  • "Flooded" or Wet Lead-Acid batteries have removable caps on the cell tops to allow topping up with distilled water as required.
  • Sealed batteries are sealed at the top, and thus won't leak acid when tipped over or give off gas while charging under normal conditions.
  • Note some Sealed "Maintenance Free" types still use wet electrolytic fluid, but simply have a sealed top. Their performance is similar to standard "Access" or "Flooded" lead-acid batteries however they don't need topping up with water as they use a recombinant agent inside to turn the normal gasses produced under charging conditions back to water.
  • Sealed batteries generally use a low pressure safety valve to "vent off" in the case of a battery failure or over-charging. This valve only lets the gas out quickly then automatically re-seals, sometimes resulting in a rather "sucked-in" or convex side to the battery if it has been chronically over-charged.
  • In general a good quality flooded battery (from Trojan or Century for e.g.) will be less expensive than the equivalent quality of Sealed battery so if ventilation and access to "top them up" is not an issue then they are still a good choice.
  • Flooded Lead Acid batteries, whether sealed maintenance free or accessible types, can give years of good service if charged and maintained well. Trojan is a good example and many owners report 5+ years of service.

Lead-Acid versus GEL/AGM

  • Flooded Lead Acid batteries are charge-rate limited, with higher internal resistance meaning they can not accept a charge rate (and hence charge up) as quickly as the GEL or AGM types.
  • Both GEL and AGM use electrolyte suspended in a medium (Gel paste or an absorbed glass mat respectively) instead of a liquid. They are sometimes referred to as "acid starved" and without the liquid acid they are safer in an accident situation, and of course do not give off gasses while charging normally.
  • Good quality GEL and AGM batteries also display much lower internal resistance than standard lead-acid batteries for rapid charging and the ability to provide high bursts of power - e.g. for winching applications. See the pages for Optima and Lifeline batteries for more information on this.

AGM versus GEL

  • AGM batteries use an absorbed glass matting material to hold their electrolyte and are becoming the more popular choice for sealed deep cycle batteries in RV & Marine use. The fact that leading brands such as Lifeline, Optima and Ultimate all use AGM is testimony to its advantages. AGM also performs better than GEL in very cold conditions and AGM is often less expensive than GEL like-for-like.
  • GEL batteries use a gel paste in which the electrolyte is suspended. When a high quality GEL battery from a manufacturer such as Sonnenschein (Germany) or GEL-TECH (USA) is used then very long life-spans can be achieved, and if space constraints (e.g. golf-carts) dictate that flattening the battery will happen then GEL technology recovers better than most AGM or regular Lead-acid batteries.
  • The downside for GEL, cost aside, is that it requires a lower charging voltage than typically produced by vehicle alternators and over-charging can permanently damage them so under the bonnet applications are generally not possible.
  • AGM and Lead-Acid batteries both work fine on the higher voltage levels that alternators produce, unlike GEL. This makes them a safer choice although many AGM batteries should also not be fitted under-bonnet due to case material/heat constraints.
  • The easiest solution is often to replace like for like. For example if your golf cart has a GEL charger already and you are happy with your GEL battery then its easier to replace it than to change both the charger and the battery by going to AGM. Note a GEL charger will not fully charge an AGM battery generally speaking.

Some more information on the 3 types of Fully Sealed (aka Dry Cell) batteries follows. 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). Often designed for non-cyclic applications (float or standby), SLA is now considered a slightly old-fashioned term but like "gell cell" and others its still in use.

Sealed Lead Acid deep cycle batteries work reasonably 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 Lifeline Deep Cycle range, as well as the Ultimate UL Battery Range and the Ritar AGM 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.

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 & Installation

Follow this link for more help and information on installing and charging your deep cycle battery.

Also we would be happy to provide advice on the right charger for your particular requirements. Some of our wide selection of Battery Chargers are now available online.

We also have a wide variety of fixed and folding Solar panels with associated regulators / charge controllers.