Deep cycle battery advice

[Ric]

I've just bought a couple of 70Ah Delphi Freedom Marine deep-cycle batteries for my domestic bank. I understand the idea of deep-cycle batteries is that they can be deeply discharged and then recharged without suffering too much. But is there a good practice threshold voltage below which it is better not to discharge in order to ensure maximum battery life?

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[Ric]

Another question on same subject I forgot to add. If a battery is nominally 70Ah and is "fully charged", what will its voltage be when it has yielded 70Ah? Is the theoretical capacity measured to the point where it is completely flat (ie 0v) or is there a nominal voltage which is the point where the battery is considered to be "empty".

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[Robin]

You should not discharge it more than 50% and preferably less on any regular basis. Unfortunately that means your nominal 70AH battery is only giving a useful 35AH, and that assumes it was 100% charged in the first place. If you are charging via a standard engine alternator or simple mains charger then you may not get it to more than 80% full, reducing the available power to just 25AH.

A fully charged 12v battery rested (left a few hours with no use) not being charged will show 12.6v - 12.8v. It will show about 12.2v at 50%, it is flat at 11.7v and maybe dead too! Put a heavy load on (fridge, radar) and at 50%/12.2v the battery volts might drop to below where these will work, fridges have low voltage cutouts at around 11v.

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[charles_reed]

I've one lead-calcium battery in my power banks and I have to say that it's a dog, slow to re-charge and reluctant to give up its power and with far less capacity for weight and volume than good lead/acid batteries.

Even with a smart battery charger you'll not get more than 62ah into one rated at 70ah and voltage will drop quickly under any considerable load tho' it's OK with 4-5 amps continuous.
As far as bottom volts are concerned mine stops producing any reasonable current at about 11.2 volts, but it is about x2 the size of yours.

I infinitely prefer industrial batteries which don't last quite as long but are far more efficient.

Dependant on your point of view, it's good or bad that they'll not wear out, mine is 9 years old.

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[andyball]

Victron Energy has in depth (but not too techy) explanations all about batteries & charging. Click on technical & download "Electricity on Board and other off grid applications".


<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by andyball on 20/12/2003 19:43 (server time).</FONT></P>

 

[catmandoo]

Deep cycle means that the battery can tolerate a lot more cycles of charge /discharge than an ordinary car type battery.
What you want is longer life , maximum capacity (ampere hours) and an acceptable voltage range.
Suggest you consult one of the battery management equipment suppliers such as Sterling . You cannot fully charge your battery but you can boost it so that it can absorb a lot more ampere hours that with a normal charger . I have just fitted one and it is great . Also fitted battery management panel which measures amount of ampere hours used up or input which is also great and gives a good measurement of what is actually happening plus monitoring of voltage with alarms etc . Efficient functioning of any DC devices drawing from the battery is dependant on battery voltage so there will be a point when the voltage drops to a level that they will not function or will cause damage ie to pump motors over heating etc . Which you don't want anyway. A battery is considered effectively dead when the voltage falls below 1.75 volts per cell ie 10 .5 volts for a 12volt battery.


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[poggy]

Hi,

I tend to buy cheap large capacity batteries and then change them more often. If you use large batteries you are unlikely to discharge them as much, so I think you can get away with cheaper ones. I bought a battery from Makro (about 100-120ah I think) for £29.99 + VAT and it is made by Exide. If this lasts a couple of years I will be happy. I also don't have any expensive battery charger or regulator. I think there are so many variables that for the type of sailing I do (max weekend) they won't really add much to my set up.

I do have a 950W small generator on board as well as battery pack which is fantastic for starting the engine if the batteries are flat. It even started a 4 litre Range Rover.

Poggy

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