Boats and batteries – which battery is best and how many do you need?

CALCULATING HOW MANY BATTERIES ARE NEEDED ON A BOAT:

We recently had to rethink our solar and battery power before heading off to sail the 7 seas. You can read all about our solar panel decisions here.

The batteries arrive!

Once we had worked out our energy needs, we needed to make sure we selected the right type of batteries to store our energy.

Lithium, gel or traditional flooded lead-acid batteries?

Remember, this is our personal choice and may not work for everyone, do your own homework when embarking on this expensive journey into battery kingdom.

Lithium scared us.( Especially the price). They have virtually no internal resistance and they need some fancy electronics inside them to keep them happy. The technology is there but we felt it hasn’t matured enough to make us feel at ease using them. You have to develop a whole new way of thinking about your batteries eg. traditional batteries don’t really enjoy being cycled right down to a low level whereas lithium batteries actually require that to make them last longer.

Gel batteries can only be charged slowly which doesn’t suit our smart charger alternator combination that likes to kick ass into the batteries when we run our engine.

We decided on the best-flooded lead-acid batteries we could find ….and a shitload of them (still cheaper than 2 lithium batteries).

So going back to our daily consumption of 1600 watt-hours (see the previous article), and assuming that we may need to supply our systems for perhaps 3 days of a cold front during a passage, we did the following sum: 1600 watt-hours x 3 (days) = 4800-watt hours. This is the amount of energy we need to be able to store in the batteries. Battery capacity is specified as amp-hours so 4800-watt hours (/12) = 400 amp-hours. (I failed maths but even I get the gist of this). Assuming we don’t want to discharge the batteries by more than half we decided on 6 x 150 amp-hour Trojan golf cart batteries. This gives us 900 amp-hours. Hopefully plenty!

Installing was easy as we had plenty of space, they are just bloody heavy to actually get on to the boat. So far, so good! Energy storage versus energy we are producing seems to be on the right track. It is winter in the southern hemisphere and although it’s pretty mild sunshine, we are keeping up really well. Looking forward to the summer sunshine when we can really kick some ass!

Happy sailing wherever you are!

Captain Mike and Nikki.

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