Battery types can be classified half a dozen different ways, so we will cut to the chase. On board a yacht, we need rechargeable lead-acid batteries for three different applications:

• Starting the engines
• Emergency lighting in the passageways
• Powering the equipment

These applications require different types of battery. See also layout of the batteries.

Starting, Lighting, Ignition

Starting the engines requires a vehicular-type battery that can provide a very short burst of very high current to crank the engine and provide ignition. This is sometimes called an SLIStarting, lighting, ignition (battery) battery (starting, lighting, ignition). SLI batteries are slow to recharge. Other vehicular types are traction (also called RVRecreational vehicle and marine) and stationary (also called standby and float). Traction batteries are used in golf carts and RVs.

Standby Batteries

For emergency lighting and backup power supplies, standby batteries, e.ggram., lead-calcium, are used. Typically they will provide juice to a lamp for 1.5 hours.

AAmpere (amp), SI unit of electrical current separate standby lead-acid battery for instruments in the cockpit is also a good idea.

Main House Bank

For the house bank, although traction batteries are sometimes used, what we really need is a true deep-discharge (DDDeep discharge) battery. Unlike an SLI, a DD provides high levels of current for a long period, and re-charges very quickly. Traction batteries have a slightly lower cost, but overall efficiency and performance will be better with DD batteries.

Best Practices

It is a good practice to:

• Fuse the house bank internally as well as externally. This will keep a battery gone bad from shorting and discharging the entire bank. Some batteries are built so you can replace individual cells.
• Use latching relays to remotely disconnect the batteries in the event of an electrical fire.

Construction

Flooded or Sealed

All of the above types are available in flooded or sealed sub-types. Flooded batteries are an older design. Internally they emit oxygen from the positive electrode and hydrogen from the negative one. This has to be vented to the outside to release pressure, i.e., they lose water and you have to top them up regularly. They have a relatively high internal resistance, which causes them to lose their charge by as much as 1%percent per day. During charging, they can lose 15-20% in heat losses.

Sealed batteries are just that, and they require no topping up. They use gel or absorption glass mat (AGMAbsorption glass mat) to immobilize the acid solution. Unlike flooded batteries, they are not prohibited from air shipment. Gel batteries use a thickening agent like fumed silica to immobilize the electrolyte.

AGM batteries were originally developed for use in aircraft. In AGM batteries a fine fibreglass mat between the lead plates absorbs and immobilizes the acid. This makes the acid more available, enhancing the reaction between the acid and the plates. Consequently AGM batteries can be discharged and recharged at higher amperages than other types of construction.^[1] They are also resistant to vibration, operate in any position and will survive submerging.

Gels and AGMs have a lower internal resistance, losing only 1-3% per month due to internal discharge. Gel cells lose 10-16% to heat during charging while AGMs lose as little as 4%, meaning that the charging system can be smaller.

Physical Size

All of these types are built in different physical sizes. The most appropriate size for a boat’sSecond starter and house banks is 8D. Types cannot be mixed in a house bank, because they have different discharge and charging rates. In fact, all batteries in any battery bank (not just on a boat) should be of the same brand, type and size and, preferably, batch number. Lifeline, Optima® and Rolls Surrette are typical AGM brands.

Location

Lead battery lifespan is reduced at temperatures over 77 °Fdegree Fahrenheit (25 °Cdegree Celsius, SI unit of temperature), so put the batteries low and as close to the keel as possible to keep them cool.

References

1. ↑ DC Battery Specialists, http://www.dcbattery.com/agmtech.html