Starter battery: CCA vs Ah

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fergycool

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Am I right in thinking that it's the cold cranking amps (CCA) rating that's critical for a starter battery and Ah is not that useful?

The current starter battery on my Perkins 4.270 (4.7l) is 110Ah with 750 CCA. It's no longer taking a proper charge. Just seen a good offer for a battery of 850CCA but only 100Ah. Would that work?

Nothing other than the starter motor is powered by the battery.

Thanks!
 
moodyNick said:
You are right in thinking that. The battery you have found will be fine.
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+1

I bought a starter battery from an auto factors. Cost about £60. 55Ah I think. Can't remember the CCA, but it is obviously a starter battery. Has worked fine for 5 years. Has started the engine first time every time (except when there was a blocked fuel pipe). It's a four cylinder Yanmar.

If you've got a battery that will start an equivalent engine in a road vehicle or agricultural vehicle it is good enough to start the engine on a boat.
 
fergycool said:
Am I right in thinking that it's the cold cranking amps (CCA) rating that's critical for a starter battery and Ah is not that useful?

The current starter battery on my Perkins 4.270 (4.7l) is 110Ah with 750 CCA. It's no longer taking a proper charge. Just seen a good offer for a battery of 850CCA but only 100Ah. Would that work?

Nothing other than the starter motor is powered by the battery.

Thanks!
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What do you mean by "no longer taking a proper charge". Is it having trouble starting your engine, or do you merely get a sense, or a monitor, which suggests it might not be fully charged.

e.g. If your engine draws 750A for 10 seconds to start, (and 10 seconds feels like a long time when starting an engine, so this is pessimistic), It will use 750 divided by 60, divided by 6, which is about 2Ah. The alternator will replace this fairly quickly after a bit of motoring, so it should be regularly replenished.

If it is having trouble starting the engine, it might be shot, (but could be poor connections or something else), and you may need a new battery. A big CCA is the thing to buy, as the Ah rating of most batteries will easily cope with the couple of AH drawn each time you start - as long as you usually run the engine for a while after starting it.

I think some people have deliberately chosen very small batteries with high CCA, say, 50Ah, to save space.
 
Richard10002 said:
What do you mean by "no longer taking a proper charge". Is it having trouble starting your engine, or do you merely get a sense, or a monitor, which suggests it might not be fully charged.

e.g. If your engine draws 750A for 10 seconds to start, (and 10 seconds feels like a long time when starting an engine, so this is pessimistic), It will use 750 divided by 60, divided by 6, which is about 2Ah. The alternator will replace this fairly quickly after a bit of motoring, so it should be regularly replenished.

If it is having trouble starting the engine, it might be shot, (but could be poor connections or something else), and you may need a new battery. A big CCA is the thing to buy, as the Ah rating of most batteries will easily cope with the couple of AH drawn each time you start - as long as you usually run the engine for a while after starting it.
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If I use a smart charger (CTEK) for 24 hours then the battery displays 12.7v when disconnected. However, it will turn over the engine for about 10 seconds then nothing. The engine is not starting. After this single attempt the voltage on the battery drops to 12.0v. Subsequent times it turns over a low slower if at all.

If I jump from the other starter battery (twin engine, twin starter batteries) with just a single lead between the two +VE terminals of the batteries (there are heavy duty cables from the -VE of each battery to each engine) the engine starts almost immediately.

To me that signifies that the battery is gone and the cables/starter motor is likely fine. Would you agree?
 
CCA is indeed the most important parameter for engine starting, there are however some other considerations. On a boat it may be useful to have a battery that can provide a useful amount of domestic power in an emergency. There is also difficult starting to consider. A larger battery will be generally a more durable one too. Prolonged starting can buckle and overheat a small battery.
 
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Richard10002 said:
I think some people have deliberately chosen very small batteries with high CCA, say, 50Ah, to save space.
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But this can be taken too far! I bought a Red Flash 900 for a starter battery small enough to mount in the tunnel alongside the gearbox. The CCA was adequate for the starter motor, particularly as the temperature is always on the warm side, summer in Greece. However, the capacity is only 13 Ah and this proved inadequate if the battery was slightly run down. It was an experiment that was only partially successful. A replacement Red Flash 1100 with a capacity of 35Ah is on its way out there right now. It seems that the 900 is no longer available, not listed on the DMS site.
 
vyv_cox said:
But this can be taken too far! I bought a Red Flash 900 for a starter battery small enough to mount in the tunnel alongside the gearbox. The CCA was adequate for the starter motor, particularly as the temperature is always on the warm side, summer in Greece. However, the capacity is only 13 Ah and this proved inadequate if the battery was slightly run down. It was an experiment that was only partially successful. A replacement Red Flash 1100 with a capacity of 35Ah is on its way out there right now. It seems that the 900 is no longer available, not listed on the DMS site.
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More or less proves the point I made
 
savageseadog said:
More or less proves the point I made
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Except that 13AH is really small. 35AH is more than enough. Typical conventional engine start batteries are in the range 55-80AH. If you flatten one of those starting then then there is something really wrong with your engine. Best setup is to have large capacity house bank which can be switched to start in emergencies, but not to use engine start for domestic.
 
I agree, 13 Ah is very small. I believed it would be sufficient for a relatively small engine, 800 cc or so, in good condition and normally starting on first turn of the key. For the first season it was, but then my solar panel regulator became faulty and was not charging the second battery, of which I was unaware. This caused the battery to be in less than ideal condition and it was no longer 100% reliable. Last season we effectively had only the domestic bank, which is plenty big enough to start any engine.
 
fergycool said:
If I use a smart charger (CTEK) for 24 hours then the battery displays 12.7v when disconnected. However, it will turn over the engine for about 10 seconds then nothing. The engine is not starting. After this single attempt the voltage on the battery drops to 12.0v. Subsequent times it turns over a low slower if at all.

If I jump from the other starter battery (twin engine, twin starter batteries) with just a single lead between the two +VE terminals of the batteries (there are heavy duty cables from the -VE of each battery to each engine) the engine starts almost immediately.

To me that signifies that the battery is gone and the cables/starter motor is likely fine. Would you agree?
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Yes :)

Sorry if I seemed a bit pedantic. I was going to go on to say that, if you try another battery and it works, ( or doesn't), you will be pretty sure, one way or the other.

Having been sold a few batteries in my lifetime, only to find it wasn't the battery.........
 
ditchcrawler said:
I have been using the Red Flash 1100 to start my Volvo 2003 (28HP) for 7 seasons and hope to get another year out of it.
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My Red Flash 1100 has been lying on its side in the bilges for ten years and is still starting my 56HP 4 cylinder Yanmar. It is only ever charged by a 5 watt solar panel here in the Med.
 
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