Buyer’s Guide

Take charge of your battery bank

How hard could it be to replace a 12V boat battery? Well, as Sam Fortescue discovers, there’s a world of choice to navigate

It will probably sneak up on you, the realisation that you need to replace your boat batteries. Perhaps you’ve had a few narrow squeaks cranking the engine, or noticed how the lights on board dim whenever the water pump kicks in. Like most components on a boat, batteries have a natural life. They may eventually fail spectacularly, but until that happens, their performance will increasingly suffer.

If you were happy with your previous lead-acid batteries, and they lasted five or more years, then the easiest thing is simply to replace like for like. One of the trickiest elements of installing new batteries can be ensuring they fit into a tight space, and that the existing cables will fit the terminal layout. By using identical batteries, you can be sure of this (just check that the design hasn’t changed). Frustratingly, there are no standards when it comes to battery dimensions or terminal positioning.

It is critical to replace all the batteries in the same bank at once. System performance is limited by the weakest battery in the bank, so the older ones will quickly wreck the new.

Time for change?

It is a big expense to replace good marine batteries – prices start around £100 for a 100aH wet-cell and range up to three times that for a top-quality gel or AGM. And bigger boats will have bigger battery banks, multiplying the cost further. So you want to be sure you’re buying exactly what your boat needs.

If you have added extra electronics to the boat or want to run longer on batteries between charges, it would be worth looking for batteries with more capacity or better performance that still t the space available.

Chemistry is constantly improving to produce more robust batteries, so a new unit might be better at low rates of charge or resist the sulphation that begins to occur when a battery is allowed to run at. It might allow faster recharging and resist the self-discharge from which all lead-acid batteries will su er to some degree.

Types of battery

Most boats still use lead-acid batteries – where sulphuric acid reacts with plates of lead to release electrons. You will typically have a dedicated starter battery for the engine, and a bank of one or more ‘house’ batteries to run everything from the navigation systems to the fridge. ey both do di erent jobs, and will o en be di erent types of battery. e engine cranker needs to be able to supply huge amounts of amps for the few seconds before the engine res. With a Cold Cranking Amperage (CCA) rating of hundreds and sometimes more than 1,000A, these batteries will have thin plates for minimal internal resistance. ey should never discharge more than a few percentage points, and will be badly damaged by regular deep discharge.

House batteries are normally deep-cycle batteries, meaning they're designed to be discharged by 40-70 per cent between charges. ey have thicker plates for greater robustness and the ability to keep supplying moderate current at a steady rate to all the on-board consumers.

e battery for a windlass, winch or a bow-thruster will normally be somewhere between the two: suitable for more prolonged use, reeling in anchor chain or manoeuvring out of a tight berth, but able to provide high spikes of current.

Across these basic applications, there are three basic avours, each with their advantages and drawbacks. e cheapest and simplest is the wet-cell battery, whose acid sloshes around inside. It vents hydrogen and oxygen when charging and needs to be kept topped up with distilled water. It must also be installed upright and can release corrosive sulphuric acid mist.

Germany’s Sonnenschein developed a superior maintenancefree type of lead-acid battery in the 1950s which is still with us today. Gel batteries contain the acid electrolyte in a gel form, combined with silica, and are sealed, so no topping up is required. However, they are more sensitive to uctuations in charging current, and are best used with a speci c gel charger. ough they usually absorb less power than AGM batteries, they retain that charge well and discharge themselves much more slowly.

More recently, absorbed glass mat (AGM) batteries have emerged, where the acid is held between glass bres by osmosis. ey can be installed on their sides and need no topping up. ey are the most resistant to temperature uctuations and vibration and are said to be safer, because they recombine the oxygen and hydrogen produced during charging more quickly back into water. ey also have lower internal resistance, which means higher currents and greater e ciency.

Further re nements of the AGM type have emerged in the last few years. America’s Odyssey brand uses ‘thin plate pure lead’ technology to build more e cient batteries that last longer and resist temperature extremes better. Other manufacturers from Victron to Ritar put carbon or graphene into the lead to prolong the life of the plates at deep discharge.

Gel batteries are among the most expensive, typically costing 2.5 to 3.5 times the cost of a basic wet-cell – that is, up to about £350 for a 100aH capacity. AGMs cost £200-£300 for a 100aH unit. deep-cycle batteries, meaning they're designed to be discharged by 40-70 per cent between charges. ey have thicker plates for greater robustness moderate current at a steady rate to

ABOVE L-R

Sonnenschein and Odyssey batteries

BELOW L-R

e Victron and Ritar Expedition Plus range

Looking a er your batteries

It doesn’t take long to wreck a new battery. But with a little bit of maintenance and careful use, they should last ve or more summers. First and foremost, ensure that you have a good quality battery charger on board to keep the batteries topped up.

It should have a mode designed for your battery type – wet-cell, AGM or gel – and a 3-step charging regime to suit. Make sure it is using the voltage speci ed by the battery manufacturer. It should also have a temperature sensor to adjust charging regimes accordingly. is is one reason that all batteries in a bank should be located in the same area.

If you can’t simply plug in to the mains in a marina, you’ll need to think about alternatives. Some

BATTERY COMPARISON TABLE

Brand Model

Type Ah (20hr) Cranking current Lifecycle (50%) Price 2021 EN (0 deg)

Lifeline GPL-31T AGM 105 750A 1050 £410.00 Odyssey AGM31A AGM 100 1150A 900 £298.47 PowerMax 100 Sealed Flooded 95 700A n/a £104.00 PowerMax 110 Leisure Flooded 110 630A n/a £97.38 Rolls S12 AGM 105 820A 1200 £239.03 Rolls R12 AGM 100 900A 800 £207.37 Varta Pro LFS105 Flooded 105 800A 200 £138.00 Varta LA105 AGM 105 950A 400 £190.00 Trojan 31-GEL Gel 102 620A 1000 £360.00 Trojan 31-AGM AGM 100 600A 1000 £265.00 Optima BlueTop D31M AGM 75 900A n/a £224.00 Numax CXV30HMF Flooded 105 940A 500 £89.00 Leoch Powabloc GTP12-110 Gel 95 800A 2000+ £200.00 Sonnenschein GF12094Y Gel 110 760A 800 £292.50 Exide ES1350 Gel 120 760A 800 £240.00 Victron Lead Carbon AGM 106 500A 1500 £306.60 Ritar Expedition Plus AGM 110 1000A 1375 £160.00

people take their batteries home with them for charging, but this only really works on small boats.

You can use renewables to charge the battery, but these are obviously not always reliable. Some powerful wind turbines can’t tail off output to suit the battery’s state of charge – they are either off or on. Solar panels provide a more stable output, but usually at much lower rates of charge.

You also need to make sure that you’re not overusing your batteries. Even top-of-the-line deep cycle batteries do not like to have more than about 60 per cent of their power regularly drained. Otherwise, life expectancy (number of cycles) drops away quickly.

US battery maker Concorde, whose brands include Lifeline, says that its units should manage around 1000 cycles to 50 per cent discharge. Raise the depth of discharge to 60 percent, and cycles fall to 800. Cut it to 40 per cent and you get 1,500 cycles before you have to replace the batteries. Cranking batteries are even more sensitive.

Lifeline

Built entirely by hand, Lifeline AGM batteries meet military specifications. Manufacturer Concorde says that this superior construction gives them lower internal resistance than others and means 20 per cent faster charging.

Varta

Pitched more at the motorboat market, Varta manufactures marine AGM and wet-cell batteries in plants in Europe and America. It produces a ‘dual purpose’ line designed to crank the engine and provide power for on board systems.

Optima

Also built by the company which owns Varta, Optima batteries have a distinctive rounded shape to each cell. They are all AGM varieties and have a reputation for durability, especially the Bluetop model, recommended for marine use. Best suited to smaller boats because of a 75Ah maximum size, they are relatively pricey.

Rolls

Rolls’s distinctive, red-cased batteries include the new FS series, which is a high-capacity conventional wet-cell particularly designed for marine use. Thick plates and a high-density active paste make the battery more efficient and reduce the discharge rate. The batteries have a double exterior skin and carry up to 10 years’ warranty. They are made in Canada.

BELOW L-R

The Lifeline, Varta, Optima and Rolls batteries

LITHIUM-ION BATTERIES

Lithium-ion technology overturned a century where lead-acid batteries were the only option. There are several chemistries available, but lithium-iron phosphate (LiFePO4) has emerged as the best compromise between performance and safety. The advantages are clear: fast charging, very deep cycling across the full power range, long service life and as little as 30 per cent the weight and bulk of a lead-acid system. Weighed against that is mainly the cost, although there can be safety issues if the lithium cells are breached or incorrectly charged. Lithium batteries require a specific charging regime and battery management system to monitor them. Charging voltages are more precise than with lead-acid batteries, and the current much higher because lithium absorbs charge faster. Brands such as Mastervolt and Victron offer plenty of off-theshelf combinations. Victron’s SuperPack is a battery that contains all the components required – just plug it into a suitable charger. Costs are around £1,000 for a 100aH, 12V equivalent battery. A cheaper Chinese lithium battery like the 100aH unit from TN Power costs £700 to £800 depending on whether you want Bluetooth connectivity. Both weigh around 14kg.

Victron Energy

Victron’s AGM and gel batteries use clever electrochemistry to provide a series of benefits for sailors. Lead calcium grid material means that the batteries are very slow to discharge when left or stored. They lose just 2 per cent per month at 20 degrees C compared to an industry standard of 5-10 per cent.

The gel batteries in particular are very resistant to abuse. They can manage 2,500 cycles at up to 50 percent discharge, or 1,500 at 80 percent discharge. The SuperCycle AGMs can be fully discharged more than 300 times without dying, and offer 1000 cycles at a more usual 40 per cent discharge

Trojan

Another well-known US brand of batteries, Trojan now has a gel series to go alongside its existing AGM and wet-cell lines. Its basic wet-cell batteries can be connected up to a network of pipes which allow you to rewater them all at the same time, without spills.

Trojan has a unique sealed variant of its wet-cell battery, containing a proprietary carbon additive to speed up charging times and improve charge retention. So-called ‘smart carbon’ is particularly useful where recharging cycles are incomplete because of reliance on renewables.

It has pulled the features of its AGM line together under the C-Max umbrella. This boils down to a thicker, metallic paste between plates, a stronger grid, and Maxguard separators between anode and cathode to extend battery life.

Numax

Introduced in 2002 by the British battery supplier ManBat, the own-brand Numax line covers AGM, gel and classic wet-cell batteries.

Sonnenschein

Known as the German brand which first developed gel batteries, Sonnenschein is now a subsidiary of Indian-owned Exide.

PowerMax

The Leisure range includes calcium to reduce self-discharging when the battery is not in use, and is available in a ‘maintenance-free’ sealed version, despite being wet-cell. They have thicker plates for deep cycling a magic eye hydrometer, and dual terminals for easier fixing. This is Barden’s ‘own label’ battery.

Odyssey

This brand belonging to US manufacturer EnerSys has now started producing the thin-plate pure-lead batteries previously supplied by NorthStar. Their AGM batteries are billed as all-rounders that are capable of very deep discharge and high cranking power.

Leoch

This Chinese battery maker with factories across Asia produces a line of gel tubular plate AGM batteries with an impressive lifespan of 1200 cycles to 80 per cent discharge. It also does value lithium products.

ABOVE L-R

The Trojan and Numax batteries

BELOW L-R

The Powermax and Leoch batteries

WHERE TO BUY BATTERIES

Barden-uk.com Tayna.co.uk Alpha-batteries.co.uk Battery2u.co.uk Allbatteries.co.uk