Duncan Kent investigates a range of the best marine batteries for quality deep-cycle usage available today
Good quality, deep-cycle house batteries are not only a sound investment, but also an important safety factor when cruising. There’s a great deal of misleading nonsense spoken and written about batteries, so be wary when you buy – especially online. Many so-called ‘leisure’ batteries are a poor compromise between a cheap starter battery and a heavy-duty one and are not suited to regular deep cycling so it can be hard to find the best marine batteries for these purposes.
Traditionally, heavy-duty Flooded Lead Acid (FLA) batteries were always used for the house bank, but they’re very heavy and require regular topping up. They can also produce dangerous quantities of hydrogen gas whilst charging.
Today, some boat owners are fitting Lithium-ion batteries (usually LiFePO4), for their capacity to recharge quickly and ability to be almost totally discharged without damage. However, they’re expensive and often require a system redesign, so good quality Absorbed Glass Mat (AGM) sealed batteries are a sensible compromise.
With their electrolyte absorbed into matting rather than free flowing, AGMs are virtually maintenance-free. They will accept a higher charge current than FLAs, shortening recharge times, and they’ll survive many more charge/discharge cycles. They also have a lower self-discharge rate, so can be left without charging for a considerable time.
Buying a known brand from a UK supplier should ensure you obtain sound advice and a genuine guarantee. A proper deep-cycle battery will be labelled with a capacity rating such as 120Ah (C20). This means (theoretically) it could endure a 6A draw for 20 hours, although there are other factors to consider.
The number of deep cycles a battery can survive is another key factor. Some quote ‘up to 3,000 cycles’ in the blurb, failing to add, ‘when only discharged 20% each cycle’.
‘Can be discharged 80%’ is another common quote for AGMs, without mentioning that if you do you could halve its lifespan. Not discharging them below 50% will extend the lifespan of all LA battery types considerably.
Best Marine Batteries
Firefly oasis carbon foam
Said to be able to discharge regularly to 80% DoD without damage and to be left semi-charged for long periods, Oasis carbon batteries have a high resistance to sulphation so are less affected by partial charging commonly found in marine applications.
Having a very low internal resistance means they can be recharged more quickly than most regular AGMs and their Microcell foam grid design has been specially developed to allow maximum energy throughflow.
Oasis batteries are also robustly built and highly vibration resistant, as well as very temperature tolerant, which is ideal for the vagaries of a marine environment. Being a relatively new technology, however, these claims of durability and longevity have yet to be entirely proven, although current tests results look promising.
Currently available in 4V (450Ah) and 12V (116Ah) versions only.
Stated cycles to 50%: 3600
Capacity range: 116Ah or 450Ah
Warranty: 2-6 yrs
RRP: £499.00 (12V/116Ah)
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Leoch pure lead-carbon
One of the more recently launched, high energy-density AGMs, which utilise carbon in their plates to reduce sulphation and extend their overall lifespan.
Thin-plate, pure lead and carbon technology with advanced, punched-plate construction and double electrolyte pasting, allow the LDC range to perform better than many regular AGMs, even in a partially charged condition. It also means they can be more rapidly recharged than standard AGM batteries.
The makers state these batteries can be safely discharged down to 80% DoD, although 50% will give you a more impressive (and economic) lifespan of around 2,000 cycles.
Cycles to 50%: 2000
Capacity range: 210-400Ah
Warranty: 5 yrs
Renowned worldwide for its deep-cycle marine batteries, Trojan has been developing and tweaking its AGM range for many years and is now a goto brand for reliability in marine electrical installations.
Its latest Motive AGM range incorporates C-Max technology wherein the active plate material adheres to its thick, heavy-duty grids to supply concentrated slow-burn energy, while double-insulated, multi-ribbed separators maximise the charge flow between the plates for optimal power.
Their maximum charge rate is 20% of their C20 capacity, enabling a considerable reduction in charge time over many budget AGMs, and they can also provide sufficient cranking amps (CCA600 for the type 31) to start a small to medium size marine diesel if required.
Stated cycles to 50%: 1000
Capacity range: 89-140Ah
Warranty: 1 yr
RRP: £279.99 (100Ah)
Rolls batteries have long been recommended by cruising yacht owners for their reliability and endurance.
Purported to be capable of a 60%-80% discharge depth, the Rolls S-Series deep cycle AGM batteries feature thick, heavy plates with a high density of active material and microporous separators, allowing plenty of reserve energy to be stored deep within the battery.
These shock-resistant batteries are said to give up to 1400 cycles when discharged down to 50%, or a massive 3,500 cycles if only discharged by 20% before fully recharging. Their low resistance allows rapid, high-current charging and they can also safely be used as an occasional cranking battery for emergencies, without damage.
Stated cycles to 50%: 1400
Capacity range: 95-160Ah
Warranty: 3 yrs
RRP: £223.65 (105Ah)
These AGMs have been around for a couple of decades and have proven themselves successful in the commercial, military and leisure marine markets the world over.
Made in the USA, they are robustly constructed using fully sealed polyethylene separators and welded intercell connectors, making them ideal for sea-going boats.
Being low-resistance, they are quicker to charge than FLAs, and can be safely deep-cycled to their lower DoD threshold regularly, even below if only occasionally and fully recharged soon after. Their self-discharge is also one of the lowest at around 2% per month.
Not the cheapest AGM around for sure, but certainly one of the toughest and most dependable.
Stated cycles to 50%: 1000
Capacity range: 33-255Ah
Warranty: 5 yrs
RRP: £396.00 (100Ah)
Fullriver batteries are robustly manufactured using 99.9% pure lead cast grid plates and partition-locked bus bars. This gives them the ability to provide up to 1300 deep cycles to 50% DoD, although they can be discharged lower without damage, but at the expense of a reduced overall lifespan.
Having a very low resistance they will happily accept a high charge rate of up to 35% of their C20 charge capacity (0.35C), making them much quicker to recharge than standard FLA batteries.
Epoxy-sealed Fullriver AGMs incorporate recombinant technology that eliminates off-gassing, so they can be installed in non-vented lockers.
Good value for money and gradually becoming more easily available in the UK.
Stated cycles to 50%: 1300
Warranty: 5 yrs
RRP: £279.99 (105Ah)