Thinking of a new Battery?

[Coddy]

Came across this and I thought it might help those who are considering buying a new battery for the boat.

 

Anatomy of a Typical Battery

In recent times there have been advances in battery technology and VRLA batteries have become very popular. VRLA stands for valve regulated lead-acid and is the designation for low maintenance lead acid batteries, also called recombinant batteries. VRLA batteries are commonly further classified as:

• Absorbent glass mat battery (AGM)
• Gel battery

These batteries are often called sealed lead-acid batteries, but this term is misleading. A sealed battery would be a safety hazard due to overpressure risks when overcharged and there is always a safety valve present, hence the name valve-regulated. Sealed is opposed to vented (also called flooded). Because VRLA batteries use much less electrolyte (battery acid) than traditional lead-acid batteries, they are also occasionally referred to as an “acid-starved” design.

The name “valve regulated” does not wholly describe the technology; these are really “recombinant” batteries, which means that the oxygen evolved at the positive plates will largely recombine with the hydrogen ready to evolve on the negative plates, creating water–thus preventing water loss. The valve is strictly a safety feature in case the rate of hydrogen evolution becomes dangerously high.

One result of this design is a much higher ratio of power to weight than large, flooded type battery systems; another is a high-rate power capacity, though of relatively short duration. As a result, VRLA batteries are frequently employed in UPS or other high-rate applications.

Batteries can be subdivided further by application. They are many jobs batteries are asked to perform but the everyday jobs can be listed as follows:

Engine Starting

Lead acid batteries designed for starting engines are not designed for deep discharge. They have a large number of thin plates designed for maximum surface area, and therefore maximum current output, but which can easily be damaged by deep discharge. Repeated deep discharges will result in capacity loss and ultimately in premature failure, as the plates disintegrate due to mechanical stresses that arise from cycling. A common misconception is that starting batteries should always be kept on float charge. In reality, this practice will encourage corrosion in the electrodes and result in premature failure. Starting batteries should be kept open circuit but charged regularly to prevent sulfation.

Deep Cycle

Specially designed deep-cycle cells are much less susceptible to degradation due to cycling, and are required for applications where the batteries are regularly discharged, such as Photovoltaic systems, electric vehicles and UPS systems. These batteries have thicker plates that can deliver less peak current, but can withstand frequent discharging

Marine/Motorhome batteries, sometimes called “leisure batteries”, are something of a compromise between the two, being able to be discharged to a greater degree than automotive batteries, but less so than deep cycle batteries.

Sizing Your Deep Cycle Battery

The chart below shows some typical examples of calculations necessary when trying to size your deep cycle batteries.

 

Description Watt @12V   Amps X hrs/day =   Ah

Autopilot                 20         1.67       5.0            8.33  

Echo Sounder        4           0.33       7.0            2.33  

Instrument Lamp    10         0.83       5.0           4.17  

Log                         2           0.17       7.0           1.17  

Nav. Lamps            80         6.67       6.0           40.00  

VHF Transmission  50        4.17       0.2            0.83  

VHF Reception        5         0.42       5.0            2.08  

Fridge                    55         4.58       8.0            36.67  

Bilge Pump            50         4.17       0.1            0.42  

Sink Pump             50         4.17       0.3            1.25  

FM Radio               40         3.33       2.0            6.67  

TV                          40         3.33       2.0            6.67  

Reading Lamp       15         1.25       3.0            3.75  

Sundry                   60         5.00       3.0           15.00  

 

TOTAL        129.34

 

The total load in this scenario is 129.34Ah. Unfortunately you can not use a 130Ah battery as the battery will not be able to provide a useful voltage at 100% discharge. The recommended maximum depth of discharge for optimum battery performance and life is 50%. Therefore in this example you should have a minimum battery capacity of 260Ah. This can be made up using one very large 12V battery or multiple smaller batteries.

It is important to remember most manufacturers recommend a maximum of three batteries in parallel. This is to avoid battery imbalance which can occur during normal cycling.

[Brian]

I think the calculation of the size of battery required isn't correct for a motor boat.

Things like autopilot, nav lights etc. Would only be on when the engine is running.

[Rob]

My thoughts too Brian, as any engine running time would negate any drain and top up the battery.

 

The numbers are copied from a generic boat, possibly sailboat.

 

Plus having 2 batteries where you can emergency parallel should you flat your starter battery is a good get out of jail card.

 

I have just added a second battery, but for specific reasons have not split them as starter and auxiliary (1, 2 or 1+2). Which is fine having had a single one for 10 yrs and I have the ability to manually start the Yamaha.

[Brian]

Here's my system.

 

 

[Mike Fox]

Interesting Dave.

I'm having some weird things happen with batteries and charging at the moment, and am suspecting my mains charger is being silly.

If I ever want to be out for longer periods I know I'm going to have to be better at battery management....or running the engine quite a lot!

 

Mike

[Coddy]

I think many people are missing the point of the list. I see so many people asking "how many amps does this or that draw?" "How long can I run xxx without draining the battery?"

 

Don't forget that the list was NOT made up by me but from one of my battery suppliers. I think it also applied to motorhomes which is where some of the heavy drain could occur.

 

I just thought it might help those who are not so "electrically savvy" as others.

 

It also goes to show that using a "Leisure" battery as a starting battery is not a good idea for long liveability

[Brian]

Just pointing out that the list needs to be used as a guide, but modified for individual requirements.