battery selection questions

[docksider275]

I have two different questions/applications here:

1. I need to replace my battery on a boat where the battery only powers bilge pump and lights and the outboard (Yamaha 15) has recharging alternator. It seems a deep cycle or other marine battery could be overkill and a lighter battery would save weight. Any reason not to go will a smaller car battery or even a U1 (lawn tractor type)?

2. Have older 35 HP Johnson with elec start that also needs a new battery. Does this really need a marine battery or would a car battery do just as well (yes, I have the adapter dealies to create "marine" posts). In other words, other than size (e.g. group 24) and wing nuts on the posts, is there a difference between a marine starting battery and a car starting battery?

Thanks,
d

 

[docksider275]

Re: battery selection questions

Bump. Didn't want this to go to page two w/o a reply. I'm hoping some of the many knowledgeable people here can weigh in on these questions.

thanks

 

[bruceb58]

Re: battery selection questions

Personally, I would buy a marine deep discharge battery rather than a marine starter battery. It will last longer and can tolerate deeper discharges. You don't need the start current that a starting battery provides since you are only starting an outboard.

 

[docksider275]

Re: battery selection questions

Thanks for that information.

 

[flargin]

Re: battery selection questions

you might be able to support even the smaller battery forms (motorcycle etc). Just make sure you have your rope in shape in case you burn out the battery and cannot start with the smaller battery. the small ones have anywhere from 10 to 20 AH, vs 100AH for the larger sizes.

but yes, they are 10 lbs vs 40lbs

 

[docksider275]

Re: battery selection questions

Good points Flargin and Bruce. For the bigger boat and motor (35 hp), the battery weight is not so much the issue So unless I had a much cheaper alternative for a starting battery, Bruce's suggestion to go deep cycle (not monster size, I'd guess), would make sense. It's nice to know the demand starting my OB is so low.

For the other boat with the rope start 15 HP, it's a question of weight and space (my switches and fuses for lights and bilge pump are all in/on my battery box). I had had a group 24 deep cycle in there, but the smaller size would make it easier to close the box and be lighter in the boat. All fine if sufficient to power the bilge pump between outings in the boat (which is docked at the lake cabin all summer). Hmmmm. I guess I should look again at the amp draw of my little bilge pump and do some math of some kind?????

 

[Boatist]

Re: battery selection questions

I would go with a group 24 auto starting battery because they are cheaper and places like Cosco or Wal-Mart have a 3 year free replacement and 100 month pro rated warranty. Other auto starting batteries even smaller than a group 24 are ok also but get the best price you can fine. I would not get a motor cycle or lawn mower battery. Smaller batteries are lighter but usually not much cheaper. Deep cycle batteries usually only have a 1 year free replacement and 3 year pro rated.
To make the battery last a very long time make sure it is fully charged at the end of each trip. Also charge at least every 2 month is hot weather when it has not been used. Charge every 3 month is winter used or not.

 

[docksider275]

Re: battery selection questions

Well, I made one decision after weighing all of the perspectives offered here.

For the 15 HP rope start Yami on 14' boat, I opted for a smaller starting battery. It is a nice compromise in weight and price between the tractor battery and a deep cycle group 24. I also like the extra space in the box. With three switches and a power outlet mounted on the lid of the box, there's a lot of wires and they fit without protest using this slightly smaller battery.

I think I'll be all right. Except for overnight running of the auto bilge pump, all the rest of my electrical use is or can be while the engine is running (with an alternator), so I'm not likely to get stuck. Also, the battery is really critical only for running lights. I remember how to drain and bail a boat.

Thanks for the help.