batteriesChoosing batteries for your boat

These days it seems the internet is the first place most people refer to for information and advice on just about every product or service imaginable.
Unfortunately the easy access to posting information and opinion brings with it an increasing amount of misinformation, and sometimes just plain wrong advice from every keyboard expert in the land.

Batteries are a good case in point, and deep-cycle batteries in particular. Island Batteries clear up some of the confusion and provide readers with advice to ensure they aren’t left high and dry with dead batteries in their boat, caravan or 4WD.
Island Batteries, Tasmania’s own expert battery company are affiliated with R&J Batteries Pty. Ltd, one of Australia’s largest battery supply companies. Their extensive product range includes some of the world’s best-known battery brands including AC Delco, Delkor, Optima and Fullriver, to name a few. Their strength lies in the combination of proven-quality brands combined with industry-leading expertise and advice to ensure customers get the best possible battery for their chosen application. Products are available state-wide, with company stores in Hobart and Launceston, and distributors in all major centres.
In this article we look at batteries for electric outboard motors, now commonly used in fishing boats for their quietness. Only deep-cycle batteries should be used on electric outboards. Unlike automotive starting batteries which are designed to produce high output for just a few seconds (to start your engine), deep-cycle batteries are designed to provide a steady output of electrical current for a much longer period, such as that required to run an electric motor for several hours. Automotive batteries are designed to be maintained at or near 100% charged at all times. Your car battery may go from 100% down to 97% to start your engine, and then the alternator tops it back up to 100% within a short distance of driving. Due to its thin plate design a starting battery will fail prematurely if used in deep-cycling applications.
If used and maintained correctly a deep-cycle battery can withstand heavy or deep-discharge and recharge many times over before it loses capacity or fails.

Deep cycle batteries fall into four main categories, all of which are essentially still lead-acid batteries:-
GEL. In Gel batteries Silica-Gel is added to the acid to form a jelly-like, non-spillable electrolyte. Gel batteries are usually the most expensive but provide the longest cycle life (number of times discharged and recharged) Gel batteries are safer than flooded or wet-cell batteries, and less-prone to sulphation damage.
AGM. Also known as Sealed Lead-Acid (SLA), AGM batteries have Absorbent Glass-Mat separators to fully absorb and suspend all free acid, making them non-spillable and explosion-resistant like Gel batteries. Deep-cycle AGM batteries can handle deeper discharge and faster re-charge than wet-cell batteries, and will usually provide a longer service life.
Sealed Maintenance-Free (SMF) Calcium SMF batteries are now very common in automotive applications. They are a flooded wet-cell battery but do not require maintenance or top-ups during their normal cycle life. Deep-cycle versions are available. They are safer than standard low-maintenance batteries, but can still leak acid if damaged, or explode if subjected to spark or naked flame.
Low-Maintenance. Standard low-maintenance batteries contain antimony which causes internal resitance (heat) and “gassing” when charging, and water loss through evaporation. Deep-cycle versions require regular maintenance, and can sulphate and expire quickly if left in a discharged (flat)state for any length of time. A low-maintenance battery will leak if tipped over, and may explode if exposed to spark or naked flame.

The following simple rules apply to all deep-cycle batteries, regardless of construction type or chemistry, to obtain the best performance and life:-

  • The less deeply-discharged the better. Ignore any advice to “Flatten it out” occasionally. This will always do more harm than good.
  • Recharge ASAP after use. Where possible always recharge fully within 24 hours of use.
  • Use the correct type and capacity charger to recharge.
  • Don’t “half-charge” or partial-charge your battery between uses. Always charge to 100%.

Information from Island Batteries.


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