Boat service batteries

[pvb]

Basically, the electrical system in a start-stop capable car means the "starter battery" is no longer purely a starter battery and must provide power to the electrical system while the engine is off, it is therefore subject to a much more variable charging regime than was previously the case and has to fullfil the requirements of a starter and a leisure battery at the same time. Given the choice, car manufacturers would fit cheaper wet batteries as before, but wet batteries can't cope with the modern charge/discharge regime as well as AGM can. The AGM batteries fitted to cars are sized as small as they can get away with and are dependent on the vehicles electrical accessory content. More toys = bigger battery.

So you agree that AGM batteries are in fact OK for starting?

 

[geem]

Sailing boats have engine electrical systems resembling cars from about a decade to 2 decades ago - they also tend to have seperate starter and house batteries. A modern car doesn't have the space and can't afford the weight of 2 batteries so opts for AGM as a compromise - they have slightly lower specific energy and higher manufacturing costs.

The start-stop technology in modern cars (primarily to reduce CO2 emissions) is not the only cause for a shift to AGM - due to the increased energy usage in modern cars, bigger batteries are now needed anyway so the AGM compromise isn't as much of an issue.

Basically, the electrical system in a start-stop capable car means the "starter battery" is no longer purely a starter battery and must provide power to the electrical system while the engine is off, it is therefore subject to a much more variable charging regime than was previously the case and has to fullfil the requirements of a starter and a leisure battery at the same time. Given the choice, car manufacturers would fit cheaper wet batteries as before, but wet batteries can't cope with the modern charge/discharge regime as well as AGM can. The AGM batteries fitted to cars are sized as small as they can get away with and are dependent on the vehicles electrical accessory content. More toys = bigger battery.

AGM batteries have been used in German cars for several years before stop start technology existed. The requirement can from a rule that batteries should be none spill in the event of an accident. If you want to install your batteries upside down in your boat then buy AGM. If you don't then buy a far more economical wet lead acid battery. My take on whether the batteries should be deep cycle such as Trojan 6v golf cart batteries or normal truck starter batteries comes down to size of the battery box. If space is limited then deep discharge batteries such as Trojans means you can discharge to 50% without shortening the battery life. If you have a huge battery box then cheaper truck starting batteries that never get dropped more than 10% of their capacity may well be as effective and long lasting

 

[PaulRainbow]

AGM batteries have been used in German cars for several years before stop start technology existed. The requirement can from a rule that batteries should be none spill in the event of an accident. If you want to install your batteries upside down in your boat then buy AGM. If you don't then buy a far more economical wet lead acid battery.

I can buy AGM batteries for about £20 more than a rough equivalent wet cell battery, so i now fit them a "standard".

My take on whether the batteries should be deep cycle such as Trojan 6v golf cart batteries or normal truck starter batteries comes down to size of the battery box. If space is limited then deep discharge batteries such as Trojans means you can discharge to 50% without shortening the battery life. If you have a huge battery box then cheaper truck starting batteries that never get dropped more than 10% of their capacity may well be as effective and long lasting

I'd mostly agree with that, but it's also important to take into account the use the boat is put to and what charging systems are fitted. My own boat only has 330ah of sealed leisure batteries, but the rarely get discharged by more than 25%, as the solar panels keep them charged during the day.

I was recently asked to look at a customers boat, with a view to fitting solar panels, as his batteries went "flat" over a weekend at anchor. He had a pair of pretty tired 125ah batteries, in a box big enough for 4 Trojan T105s. The boat spent all week in the marina, on charge, and he only sailed weekends. He needed new batteries anyway, so we went for Trojans, on the basis that they should provide enough power for the weekend and wouldn't cost a fortune more than his existing batteries. He's very happy that they do exactly that.

 

[geem]

I can buy AGM batteries for about £20 more than a rough equivalent wet cell battery, so i now fit them a "standard".



I'd mostly agree with that, but it's also important to take into account the use the boat is put to and what charging systems are fitted. My own boat only has 330ah of sealed leisure batteries, but the rarely get discharged by more than 25%, as the solar panels keep them charged during the day.

I was recently asked to look at a customers boat, with a view to fitting solar panels, as his batteries went "flat" over a weekend at anchor. He had a pair of pretty tired 125ah batteries, in a box big enough for 4 Trojan T105s. The boat spent all week in the marina, on charge, and he only sailed weekends. He needed new batteries anyway, so we went for Trojans, on the basis that they should provide enough power for the weekend and wouldn't cost a fortune more than his existing batteries. He's very happy that they do exactly that.

If you can get AGM almost as cheap as a starter wet cell sealed battery then the AGM would be a better buy. I just balk at paying more for AGM when they appear to last no longer unless they are a true deep cycle battery.
One of the problems I came across in Panama when shopping for a starter battery for my boat was that 90% of the batteries on offer were sealed lead acid. AGM were far more expensive. I managed to get a cheap open wet cell battery. I run two 110Ah batteries in series for starting a 4.4 litre Perkins, 24v. I didnt want to buy two new batteries so I installed Victron battery balancers. One between the engine batteries and a pair on the four house bank batteries. The house batteries are identical but the engine batteries are not. When on charge the engine battery balancer bleeds of amps from the higher voltage battery to the lower voltage battery. Seems to work well. On the three year old truck batteries than form the house bank this never happens as the resistance seems to be identical. A test with a hydrometer suggests after three years of hard use as liveaboard batteries that they are,still in good condition.

 

[Baggywrinkle]

AGM batteries have been used in German cars for several years before stop start technology existed. The requirement can from a rule that batteries should be none spill in the event of an accident. If you want to install your batteries upside down in your boat then buy AGM. If you don't then buy a far more economical wet lead acid battery. My take on whether the batteries should be deep cycle such as Trojan 6v golf cart batteries or normal truck starter batteries comes down to size of the battery box. If space is limited then deep discharge batteries such as Trojans means you can discharge to 50% without shortening the battery life. If you have a huge battery box then cheaper truck starting batteries that never get dropped more than 10% of their capacity may well be as effective and long lasting

I know, I work for the German car company that fits them and have to get all my electrical systems passed by the "Energie" board before I'm allowed to release them. Stop-start just exacerbated an existing problem. With the explosion of electrical functions in cars the batteries must fulfill a dual role as starter and house battery, wet cell can no longer cut it as a house battery and the other consideration with crashworthiness is also neatly solved by AGM. VRLA prevented accidental spillage but doesn't help if the case integrity is compromised. An AGM battery with enough power reserve to run the electrical systems means it can also deliver the CCA required for engine start. It is however a compromise and I remember the fights to justify the extra cost of AGM.

I personally would not bother specifying an AGM as a marine starter parallel with a house bank because I don't need it's energy reserve (it should never suffer a deep discharge) or vibration resistance - spill resistance can also come from a VRLA battery. As for deep discharge, it is primarily plate thickness that makes a battery deep cycle, not whether it is flooded, gel or AGM - Trojan is a good example of a robust wet-cell battery that can take the abuse of deep discharges (as long as it is regularly fully re-charged).

The various technologies have their advantages and disadvantages, at the end of the day it comes down to the users requirements, charging regime, battery space and personal choice. For me that means a cheap maintenance free wet cell starter and 370Ah maintenance free wet cell house batteries. Cost was a major factor, I preferred cheaper batteries and a solar charger to expensive batteries and sticking with alternator/shore-power charging.

 

[NOHOH]

AGM batteries...which wont leak or spill......and a Megapulse battery conditioner......which will prevent/reverse sulphation. I have batteries older than 10 years still working well through using one of these since new. Spend a little more...but only do the job once.

 

[geem]

AGM batteries...which wont leak or spill......and a Megapulse battery conditioner......which will prevent/reverse sulphation. I have batteries older than 10 years still working well through using one of these since new. Spend a little more...but only do the job once.

Not always the case. AGM batteries are not immune to premature failure. By contrast we had cheap Numax batteries on our last boat, a simple PWM charger and a couple of hundred watts of solar. They were still going strong after 7 years when I sold the boat. How you use the batteries and under what conditions has far more bearing than people appreciate in my experience. If you are based in the tropics with battery temperatures approaching 40degC ( something many Med based boats will be experiencing recently) then this heat alone will half battery life without any consideration as to what type of battery you use or how you use it. Add in a full time live-aboard lifestyle where batteries get more regular charge and discharge, then battery life can be considerably shorter than expected. When people here talk about how long their batteries last it needs to be quantified with where they are locates, how they maintain charge and how they use their boat/batteries in my opinion, otherwise the statement about battery life is meaningless

 

[KellysEye]

We had Trojan deep cycle batteries as house batteries because they are designed to handle continuous low loads, golf carts use them. CCA batteries are designed for short heavy loads.