THE BATTERIES, how to choose your battery

Through three examples we compile an electrical balance from three boats equipped differently. Adapt it to your particular case.
Example No.1
Day trip, return to port at night

Equipment Instant consumption Daily use Daily Consumption Amperes Hours Amperes Comfort Refrigeration 4 6 24 Pressurized water 8 1 8 Music 1 2 2 Electronics Automatic Pilot 5 2 10 GPS/Card Reader 2 6 12 VHF Emission 4 ¼ 1 VHF reception/watch 0.1 10 1 Sounder 1 4 4 Central Navigation 1.5 6 9 Total Consumption 24h 67 Amperes

Example No.2
Day trip, night mooring

Equipment Instant consumption Daily Use Daily use Amperes Hours Amperes Lighting Main cabin 2 4 8 Cabins 2 1 2 Chart table 1 1 1 Toilets 2 ½ 1 Mooring lights 1 8 8 Galley 1 ½ 0,5 COMFORT Refrigeration 4 16 64 Pressurized water 8 1 8 ELECTRONICS VHF watch 0,1 24 2,4 VHF emission 4 ¼ 1 Sounder 1 4 4 Multimedia (tele, computer) 4 2 8 GPS/Card reader 2 6 12 Central navigation 1,5 6 9 Total consumption 24h 131 amperes

EXAMPLE N°3
Navigation Longer than 24 hours

Equipment Consumption Utilisation Consumption Instant Daily Daily in amperes in hours in amperes Lighting Main cabin 2 1 2 Cabins 2 1 2 Chart table 1 1 1 Toilets 2 ½ 1 Galley 1 ½ 0,5 Navigation lights 2 6 12 Deck light 4 ¼ 1 Lighting instruments 0,5 6 3 COMFORT Refrigeration 4 16 64 Pressurised water 6 ½ 3 ELECTRONICS Pilot 4 12 48 Central navigation 1 24 24 VHF watch 0,1 24 2,4 VHF emission 4 ¼ 1 GPS 0, 5 24 12 Card reader 2 24 48 Graphic sounder 1 4 4 Radar watch/emission 2 5 10 Total consumption 24h 239 amperes

Once the assessment is made, we take a battery capacity at least equal to twice the daily consumption (ideally 3 times.) This enables us to not discharge more than 50% of the batteries (would not be supportable.)
Example 1:
In the case of the day trip boat, it takes at least 150 Ah.
Example 2:
For those who spend the night at anchor, it takes at least 260 Ah.
Example 3:
For more than 24 hours it must be at least 480 Ah.

A battery consists of plates (grids of lead) which enclose the active material in negative plates and lead dioxide for the positive. These plates, insulated from each other, are immersed in a solution of sulfuric acid and water (electrolyte.) When connecting a current source to this set (battery charger), an imbalance occurs: a plate becomes positive, one negative, the battery is charged. When one consumes the battery, the reverse occurs.
The battery capacity is always expressed in Ah for a given discharge time 20 hours (C20) for a starter battery or similar. In theory, a 100 Ah battery can deliver 100 A for an hour or 5 A for 20 hours. In practice, we must never fall below 80% capacity. This means that on a 100 Ah battery, one never goes beyond 80 Ah. By construction, a battery is designed for a number of charge-discharge cycles (between 100 and 1000) which depends on its technology. A charge-discharge cycle is a discharge of 80% capacity and recharge to 100% or two discharges of 50% of its capacity or four to 25%.

There are two types of battery. Starter batteries are capable of providing a large amount of energy for a short period of time (starting a diesel engine, electric windlass, bow thruster…) Service batteries supply electrical consumers for a long period of time (fridge, lighting, electronics…) They must withstand a longer and slower discharge before recharging.

According to regulations, the closed and open batteries should be placed in a sealed container with a vent to the open air.