Have about the same I run 3 AGM 100 amp and have no problems cost more but loose very little discharge when not used also have smart charger in boat just plug in now and then

 Ok thanks Tomcat. What's a smart charger?

I have a Minn Kota but there are lots of different ones when you first plug in it works out how high a charge to put in then charges at high rate then turns to maintenance mode for 24hr then turns off but will cut back in if voltage drops

I’ve been doing a bit of research about batteries lately, been having problems at work, so I thought I would study the subject. This has turned out to be more complex than I expected.

I am wanting to put dual batteries on my boat, but wanted the batteries to be mounted under the floor. Weight and room. So this is my plan so far. I would mount one battery in the stern, but above deck, which will be my starting battery. It will be a standard type with caps. Used for starting and this battery will also be charged by the motor.

Reason, the charging system on an outboard, unless it’s a late model, is very basic, the higher the engine RPM the higher amperage and voltage output (that’s what I have read). Sealed batteries calcium, AGM or gel, require gentle charging and controlled voltage. If these batteries are charged too hard, they can vent and lose electrolyte. Once the top of the plates are exposed, the battery is cactus, and the electrolyte can’t be replaced. The standard battery while it loses more water, its easily replaced.

I would then mount a second and third battery using sealed “deep cycle” batteries. AGM or Calcium.

Reason, they don’t produce gas, don’t lose charge at the rate of a std battery, are water proof and can tolerate being completely discharged and recharged many times, whereas the non deep cycle battery shouldn’t be discharged below 50% of its capacity, or else it will quickly deteriorate.

To charge these batteries I would buy a smart charger 5-7 stages like Ctek or Projecta. Not use the motor to charge them. Reason the motor charging system will only charge to 70-80% and as above, charge rates and voltage may be too high, whereas the smart charger will take the batteries to 100 % the smart charger will ensure that these batteries are maintained properly which may give an 8 year life.

As can be seen the starting battery has only about 40% of its capacity available, i.e. 70-80% charge of the motor down to 50% of its rated capacity. After starting the motor should replace what power it has used.

The smart charger should be used to recharge all the batteries on a regular basis, and the batteries needn’t be removed from the boat, as these chargers have controls and shut downs in case of over temps or other dangerous conditions. The charger will automatically revert to “float” mode when the battery is charged but the charger is not turned off.

Of course wire the system so that any battery can be used for starting if required.

There is heaps of info on the net, just read up.

Not sure if Id want them under the floor My system works fine so I will stick with it

I have always used delkor, my last delkor went for 14yrs without fail, even starting a grumpy motor !

But your info says your 23 you must have got when you were 9 LOL

saw a freak battery at some show somewhere and it was a delkor. from ww2 or something and it is still starting shit!! haha

Yeh good call, it was put in by my dad when it was his boat 14 yrs ago and was replaced by me at the start of this year?