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Canal Boat - - Back Cabin -

Which type of bat­tery; wa­ter pres­sure; smoke from a cruiser; how many bat­ter­ies and heat­ing hitches

Q

What are the im­por­tant things to know about the dif­fer­ent types of bat­tery that are avail­able? FIONA, via the CB website

A

TONY REPLIES: Wet open cells have re­move­able cell caps that al­low easy sam­pling for di­ag­nos­tic pur­poses and topping up with de-min­er­alised wa­ter to re­place liq­uid lost to gassing dur­ing high charg­ing volt­ages (say above 14.5v).

They are good if you have an ad­vanced al­ter­na­tor con­troller, an al­ter­na­tor set to de­liver more than about 14.5 volts, or a bat­tery charger that al­lows equal­i­sa­tion charg­ing.

They come in two types: leisure bat­ter­ies (cheaper) may use cal­cium which in­creases the volt­age at which they start to gas, but they can only stand a fairly lim­ited num­ber of charge/dis­charge cy­cles. Trac­tion and semi-trac­tion bat­ter­ies (more ex­pen­sive) may be the best buy as they are good for many more cy­cles, but only if you re­ally know how to look after bat­ter­ies. You could de­stroy a £1000+ set as eas­ily as you can a £200 set of leisure bat­ter­ies if you do not keep them fully charged.

Sealed flooded cells are sim­i­lar but you can­not get into the cells for di­ag­nos­tics or topping up. You must never ex­ceed their max­i­mum charg­ing volt­age (typ­i­cally 14.4 volts) and prob­lems are harder to di­ag­nose. The lead plates in the bat­tery may be held apart by por­ous plas­tic sep­a­ra­tors (as in cheap open cell bat­ter­ies) or they may be ‘pock­eted’ which will be more ex­pen­sive but last longer. Ab­sorbed Glass Mat (AGM) bat­ter­ies have the gaps in­side the cells filled with glass­fi­bre wad­ding im­preg­nated with the acid. They are also sealed, so harder to di­ag­nose – and you must never ex­ceed their max­i­mum charg­ing volt­age (from be­low 14 volts to above 14.5). They can charge faster, give a higher cur­rent, and have a longer life when looked after, but cost more. Gel bat­ter­ies con­tain an acid gel in­stead of liq­uid. Some have their plates in a spi­ral form for more strength and po­ten­tially longer life. But they are ex­pen­sive and de­spite their ad­van­tages, I feel, un­likely to be cost-ef­fec­tive.

For all bat­ter­ies, three fig­ures may be quoted: Cold Crank­ing Ca­pac­ity is how many amps the bat­tery can sup­ply when new and fully charged for en­gine start­ing. This is only rel­e­vant for the start bat­tery and rarely mat­ters as most boats’ start bat­ter­ies have a far higher CCA than needed.

Amp Hour Ca­pac­ity (Ah) is how many amps for how many hours a new, fully charged bat­tery can sup­ply. A 100Ah can be as­sumed ca­pa­ble of sup­ply­ing 100 amps for one hour, 50 amps for two hours, 25 amps for four hours etc.

Cyclic life is how many times you can charge and dis­charge a bat­tery un­til it fails. Best prac­tise is never to dis­charge do­mes­tic bat­ter­ies be­low about 50% be­fore recharg­ing – and you will dou­ble cyclic life. In gen­eral, to max­imise bat­tery life keep them as fully charged as prac­ti­ca­ble for as long as pos­si­ble. Con­sider them fully charged when the charg­ing cur­rent has fallen to one or two per­cent of the bank ca­pac­ity and it has failed to drop over about an hour.

An ab­sorbed glass mat

A sealed flooded cells bat­tery

A deep cy­cle ver­sion

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