battery power needed to start my engine

hi guys&gals, just a quick question for all you electrical boffins out there, i have just upgraded my outboard from a pull start to a electric start, now it says in the book that i need a 12volt batt between 70-100ah to start the thing,this makes the batt quite large and i was wondering if there was an automotive battery that i could buy instead, as these seem smaller and lighter than the ah batterys, any advice gratfully recieved :V

Be wary of a battery other than marine, which are sealed, ie less of acid leak risk, remember car batterys can be topped up with removable caps, marine/leisure are sealed shut

I don't think marine batteries are any larger than a car batt for the same amperage. My parents Honda 50 has run off a standard car batt for the last 6 years with no probs to date.

Don't forget there's a difference between the capacity of the battery in Ampere Hours, and the cold cranking capacity (CCA) in Amps.

Get yourself down to Halfords!
You get a 3 year guarantee, should you knead to replace it there should always be a Halfords near to you to get a replacement!
As for marine deep cycle batteries I take the opinion that the car type is well suited to the Rib market!
Nick

IMHO while you have the credit card out i would pick up a plastic battery box to put it in. Keeps the terminals safe etc.

As others have said - go to Halfords. My Seraider / 90hp has been running off a £40 Halfords battery for the last three seasons with no problems. I don't know which one I have got - just chose one that would fit in the battery box, looked as if it was half well sealed and I think that it was the cheapest one they had.

Just think, even the smallest car engine is going to be more difficult to turn over than a 40hp OB.

Also the duty cycle of a car battery is similar to that of a RIB - starts followed by some running and very little in the way of accessory drain.

Duncan

You don't fancy upgrading a bit further to my 5.4m do you?

As searider says,it's how your RIB is used that will determine if you can get away with a car battery.
Car batteries will work fine as long as you arn't pulling out a lot of amps on repeated cycles. Marine batteries are constructed to handle this, where as with car batteries it can cause serious damage (especially if you deplete the charge completely).
The other factor is when charging a wet cell, make sure your battery charger is not putting out too high a voltage.Often cheaper chargers put out over 14.5 volts which can lead to premature failure of the battery.
(Although these wet cells are not quite as critical as the marine Gel cells or AGM batteries where the max charging voltages should be 14.1 and 14.6 respectivley..) Unlike a car battery, overcharging of these sealed cells can actually cause the sides to cave in.!!! So always use a 3 stage charger.
Usually overcharging the car battery will just "boil off" liquid and you might find yourself topping the levels up a little more often.Just check each cell with a good hydrometer occasionaly as you are basically diluting the acid.
So if your use doesn't consume a lot of amphours (electronics/stereo/bait pumps etc. car batteries can be used. But if you have some serious kit on board I would think a marine sealed wet cell ,an AGM or Gel is the way to go.Together with a good 3 stage charger and you should be set for several years.
cheers Dal

thanks gang, so there it is then i will go down to halfords and get a battery, and i will get a box as well, i will get the smallest 12volt they have,as all it is needed for is to start the engine, nothing else, so i will get the lightest most compact, with a 3 year guarentee, that should do iy, thanks again for all the replys, you have made my decision for me :cool: