How many cranks from a battery?

[john_morris_uk]

The point is
an engine & battery in good condition, the engine will start easily,no matter if a cranking or leisure battery is employed.
i have 3 x domestic
1 x engine
all the same battery type

I agree totally and that is very similar to the set up I have fitted to our boat. Our engine usually starts almost immediately I press the start button and the only difference is that our domestic bank is 3 x 135 Ah deep cycle batteries. I keep them well charged and have a monitor that measures Ah in and out along with charging current and battery voltage. There's a smart regulator on the alternator and a smart three stage charger for when or if we are ever plugged into the mains. Getting the last few Ah back into the domestic bank takes for ever and is never worth chasing down under normal circumstances.

But this is wasn't what the OP asked and it sort of assumes that he has an engine starting problem. I suppose one might infer that he has a starting problem from the way his question is phrased but perhaps it was just an academic exercise or he was just curious about how these things worked?

 

[oldfatgit]

How many alternators give out full power for an hour without a smart charger

Yep, dead right there, however I'd hope that by trying to extend the charging time on engine (i.e. working out a minimum and exceeding it) more good is achieved than bad, particularly with a smart charging thingy from Sterling. After all the charging current is being reduced by the back EMF of the battery as its charge state is improved and the resistances in the circuit; particularly the internal resistance of the battery. In my case that is why I have fitted a digital shunt ammeter in an attempt to work out what is going in and out of the battery. Basically, assuming a battery in good physical condition and not fitted in the last century then the lower charging currents tend to result from the improved charge state of the battery. I'm luckey and have shore power for when alongside with charging via a good system. When I end up on a swinging mooring (quite likely in the next couple of years) then I will rig up a good photovoltaic cell charging system to provide the long duration top up current for all batteries.

 

[Zagato]

How does a combined deep cycle/starter battery work? There are less of them on the market apparently than there used to be! Is it a compromise of each type rather than.....

http://www.tayna.co.uk/EXV90-Enduroline-Calcium-Leisure-Battery-P8281.html

 

[john_morris_uk]

How does a combined deep cycle/starter battery work? There are less of them on the market apparently than there used to be! Is it a compromise of each type rather than..... The only one I can find is an Enduroline EXV90

As far as I understand these things, I understand it to be a compromise design. I expect someone will be along who might know the precise details.

The choice seems to be between starting batteries that HATE being deeply discharged and at the other end of the spectrum 'Traction batteries' that will withstand multiple deep discharges but are very much more expensive. Traction batteries are designed for electric fork lift trucks, electric golf buggies etc.

Again if I understand things correctly, Leisure batteries are somewhere in between without the thickness of plate of a true traction battery and with some free space under the cells to allow debris to build up without shorting cells out.