Battery advice

[Jonny H]

I need a replacment battery for my Ribcraft 4.8 with a 70 HP Tohatsu 2 stroke
I’ve not had a chance to have the rib at home since I bought it last year but picking it up this weekend
Any advice would be appreciated for what size battery i need
Thanks in advance

[Peter_C]

How much do you want to spend? Today I would only buy an AGM, or a Lithium, not a gel or flooded cell. What group size can the battery box take? Does it already have a battery box? What type of battery hold down does it currently have? What battery cable terminal connections does the boat currently have on it?

Size of the battery is going to be dependent on load. Are you going to be running a chart plotter for hours on end, say while fishing with the boat shut off? What size battery are you replacing and has it been sufficient for your past needs?

[spartacus]

Originally Posted by Jonny H

I need a replacment battery for my Ribcraft 4.8 with a 70 HP Tohatsu 2 stroke. I’ve not had a chance to have the rib at home since I bought it last year but picking it up this weekend. Any advice would be appreciated for what size battery i need. Thanks in advance

Got the same outfit.

Read this (page 31). https://www.tohatsu.com/marine/commo...nglish_web.pdf

The M70C requires: 12V 70AH/5HR, 800 (Cold Cranking Amps (CCA), in case of cold weather: 12V100AH/5HR (850CCA).

Key thing just now, and indeed before you venture out is to keep battery topped up with a trickle charger. Halfords ones are as good as any.

[Jonny H]

Originally Posted by spartacus

Got the same outfit.



Read this (page 31). https://www.tohatsu.com/marine/commo...nglish_web.pdf



The M70C requires: 12V 70AH/5HR, 800 (Cold Cranking Amps (CCA), in case of cold weather: 12V100AH/5HR (850CCA).



Key thing just now, and indeed before you venture out is to keep battery topped up with a trickle charger. Halfords ones are as good as any.

Thanks Spartacus very useful info , I’ve always admired your Ribcraft [emoji106]

[Jonny H]

Originally Posted by Peter_C

How much do you want to spend? Today I would only buy an AGM, or a Lithium, not a gel or flooded cell. What group size can the battery box take? Does it already have a battery box? What type of battery hold down does it currently have? What battery cable terminal connections does the boat currently have on it?

Size of the battery is going to be dependent on load. Are you going to be running a chart plotter for hours on end, say while fishing with the boat shut off? What size battery are you replacing and has it been sufficient for your past needs?

Thanks Peter

[beamishken]

Thats a ridiculously large battery for a relatively small engine, I'd be prety disappointed if I thought a little outboard required that much power to start it.
Just for comparison a 4.2l yanmar 6lp 315hp diesel recommends 660 cca cant understand why they speced such a large battery for a small engine.
My personal choice would be a standard automotive lead acid battery they can be replaced several times for the cost of a fancy agm battery & there is little to gain. My wifes BMW has the option of running an agm battery or a lead acid but you need to tell the vehicle whats fitted so it alters the charge profile to suit.
I doubt the alternator on an outboard is smart enough to give the correct charge profile to optimise an agm battery.

[Jonny H]

Originally Posted by beamishken

Thats a ridiculously large battery for a relatively small engine, I'd be prety disappointed if I thought a little outboard required that much power to start it.
Just for comparison a 4.2l yanmar 6lp 315hp diesel recommends 660 cca cant understand why they speced such a large battery for a small engine.
My personal choice would be a standard automotive lead acid battery they can be replaced several times for the cost of a fancy agm battery & there is little to gain. My wifes BMW has the option of running an agm battery or a lead acid but you need to tell the vehicle whats fitted so it alters the charge profile to suit.
I doubt the alternator on an outboard is smart enough to give the correct charge profile to optimise an agm battery.

I agree that’s a huge battery ...
I’ve found the one on it now the previous owner replaced and that’s an 063 46 AH 425 cca

[beamishken]

Originally Posted by Jonny H

I agree that’s a huge battery ...
I’ve found the one on it now the previous owner replaced and that’s an 063 46 AH 425 cca

An 063 is more like what I'd fit to be honest that's plenty big enough, around £ 40 and your back in business.

[spartacus]

Who am I to argue with the techs at Tohatsu?

Their engines are a bit agricultural, and I know we're talking about mid-sized engines here. I think the M60/70C is a bit of a brute to turn-over, especially from cold. I put a conventional lead battery in 086 72 AH 670 CCA back in 2017 after the previous marine one gave up the ghost and left us high and dry at Stonehaven harbour after we launched. Found the receipt, £107.

[Jonny H]

Originally Posted by spartacus

Who am I to argue with the techs at Tohatsu?



Their engines are a bit agricultural, and I know we're talking about mid-sized engines here. I think the M60/70C is a bit of a brute to turn-over, especially from cold. I put a conventional lead battery in 086 72 AH 670 CCA back in 2017 after the previous marine one gave up the ghost and left us high and dry at Stonehaven harbour after we launched. Found the receipt, £107.

Thanks Spartacus [emoji106]

[beamishken]

Battery comparison chart here
https://www.puretyre.co.uk/car-batte...ication-chart/

Find the output you want then compare prices often similar outputs are much cheaper in a different case.
Eg 096 £67.00 https://www.ebay.co.uk/itm/324000721966
I still wouldnt trust a petrol outboard that took more starting than a big diesel though

[GuyC]

I've got a Yanmar 4LHA in my boat and the standard battery requirement is a 120AH battery. It doesn't seem to give a CCA figure.

I'd follow the Tohatsu recommendation.

[beamishken]

Originally Posted by GuyC

I've got a Yanmar 4LHA in my boat and the standard battery requirement is a 120AH battery. It doesn't seem to give a CCA figure.

I'd follow the Tohatsu recommendation.

Strange they dont qoute a cca for the 4lh when its the relevant figure for starting batteries. You can get a leisure battery with a huge AH rating but a piss poor cca both the 6lp & 6ly (which is the 6 cylinder version of the 4lh) qoute 660 cca although they do qoute 120ah
If you depleted a 5 or 600cca battery trying to start a little petrol outboard
A) Its £♡ck€d and isnt going to start
B) you'd probably have burnt out the starter

[babbot1]

Is that model a tldi or carb? If tldi they require more power to keep the voltage up while cranking for the computer not to crash. My tohatsu 40 tldi requires pretty much the same battery which I thought was crazy until I found this out.

Also recommend an agm and the largest that will fit. They last years longer and don't need to be maintained as much as lead acid. They also handle deep cycling better. Bigger is better with a battery :-)
The problem is the price. Usually double but they do last twice as long in most cases. I just bought a new agm battery that states 10-12 years life on average.

[Jonny H]

Originally Posted by babbot1

Is that model a tldi or carb? If tldi they require more power to keep the voltage up while cranking for the computer not to crash. My tohatsu 40 tldi requires pretty much the same battery which I thought was crazy until I found this out.



Also recommend an agm and the largest that will fit. They last years longer and don't need to be maintained as much as lead acid. They also handle deep cycling better. Bigger is better with a battery :-)

The problem is the price. Usually double but they do last twice as long in most cases. I just bought a new agm battery that states 10-12 years life on average.

It’s a carb model

[Jonny H]

Here’s the battery spec for Yamaha and Honda if of interest Attachment 1

[Jonny H]

[Jonny H]

Not sure what happened there posted twice and can’t delete [emoji848]

[beamishken]

So yamaha recommends a battery with less than half the cca than Tohatsu, that says to me the Tohatsu recommendation is incorrect or a misprint. That takes you back to your origional thought that an 063 will be adequate which aligns with my experience.
Unless of course Tohatsu starting systems are significantly inferior to yamaha which I very much doubt.

[spartacus]

I've re-read that user manual link I supplied earlier which incidentally is for the M60C through to M140A inclusive, and it states that's the minimum battery specification. Belt and braces!

Obviously they've learnt a few things along the way. On the BFT75 (current 4-stroke) they recommend 12V-55Ah/5HR (65Ah/20HR) (CCA582A). Interestingly same engine has 44 amp high output alternator, pretty much double equivalent charging output in 4-stroke territory. Evinrude E-Tec 75hp produces 81 amps!