Correct/optimal battery spec for Honda BF75 outboard?

CW180

Petty Officer 2nd Class
Joined
Feb 12, 2012
Messages
114
Hi

I'll soon be fitting the outboard to my boat and will need to get a new battery for it.

I've got the battery still from my old one and it is in good shape but that was a 50hp yam and the battery is a little on the small side for my liking even though it has started the honda no problem so far. It's a pretty old battery too, so I don't want to take chances with such things.

What would be the correct spec battery in terms of AH and CCA for the honda? It's a 1996 model BF75.
I presume also that there's no issue at all in getting something above the necessary spec in respect of either cranking amps or amp hours? Ideally I'd have one with more amp hours I think, to give more margin for errors etc. Just in case.

The other thing is that I would then be wanting to use the old battery for running on board electrics while the engine is not running.

I've had a split charge system in my discovery before where it used a relay wired to one of the alternator wires to control the connection/separation between the two batteries, but I'm not sure how ideally this would be set up for the likes of the honda? I know you can get rotary switches that are like isolators, so should I just get one of those to disconnect the second battery from the engine when not running, and wire all the electrics to the 2nd battery?

There's a solar panel to chuck into the equation as well, which will be plugged in when the boat is on the drive, to keep the 2 batteries gently topped up.

Many thanks!
 

Georgesalmon

Lieutenant Commander
Joined
Apr 14, 2012
Messages
1,793
Re: Correct/optimal battery spec for Honda BF75 outboard?

As you said, get the largest battery you can fit and afford. Bigger won't ever hurt anything stuff will only draw the amps it needs and not take more just because its there. Its easy to get to the alternator wires on an inboard or I/O. Tough to do on an outboard and get the wires from the motor to inside the boat, don't really have an alternator anyway. Just get a battery switch with 1/2/OFF/BOTH positions for the easiest installation of two batteries. Maybe not the best or fanciest or automaic but easy to do. Wire the house loads to the switch and either battery can then be the house battery and the other will stay fresh for starting. Put your solar panel to either battery and when you have the switch in "BOTH" it will put a little juice to both because the batterys are then in parallel. Keep the switch in OFF and the solar will only put juice in the battery its attached to. You'll need one heavy battery cable to wire the neg's together on the batteries if you ever have to use the BOTH position to start the motor.
 

CW180

Petty Officer 2nd Class
Joined
Feb 12, 2012
Messages
114
Re: Correct/optimal battery spec for Honda BF75 outboard?

Very helpful thanks.
I just nipped to the chandlers and bought a rotary switch that works as you describe.

Will work all that out into a diagram, cheers!

Re' the battery itself, I'm just not sure what spec is recommended for an engine like this, ie to know if any given one I look at is larger or smaller than necessary. Also, I'm not sure if this is nonsense or not but I seem to recall people telling me at some point in the past that outboard batteries are generally not quite the same as car ones in the manner that they deliver their power.

Can't recall the details, but it'd be useful to know more if this is true, so that I make sure I get a suitable one, despite just the numbers being right for Ah and CCA.
 

Georgesalmon

Lieutenant Commander
Joined
Apr 14, 2012
Messages
1,793
Re: Correct/optimal battery spec for Honda BF75 outboard?

Marine batteries are supposed to have more sturdy supports for the stuff inside to handle the stress of the environment. So, you should stay with marine. Otherwise the only differences are "starting" and "deep cycle". Deep cycle are better for long lower discharge rates and more deep discharge and charge cycles. Now days you can get multipurpose marine batteries that do both and I use one starting type battery and one multi purpose starting/deep cycle on my boat with good results because I had them already. Next time I need new batteries I will get both as combination starting/deep cycle. My current starting battery is a group 24 and the other is group 27. New ones will both be the same size and if you are going to purchase two new ones that is what I would suggest. In the largest size you have room and money for.
 

CW180

Petty Officer 2nd Class
Joined
Feb 12, 2012
Messages
114
Re: Correct/optimal battery spec for Honda BF75 outboard?

Thanks for the info - so ideally I'd have one deep cycle one as the house battery and one starting battery?

Or two multipurpose ones as you've mentioned, in order to prevent problems if one of them has an issue. Would mean they can both do the other's job if needed so probably preferable.

I don't know what the current one I've got is since the label has come off it. It's a Lucas and I think it was a "Super 4" or something but no info on the spec. Still works well enough though.

Will speak to a local motorfactor and see what suitable ones they might have. Apparently it should be 70AH 550 CCA anyway.
 
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