Which battery to buy - 1963 Johnson 40HP RDS-25D

[grumpyguy]

So bought an old boat motor combo dirt cheap. All in good shape. Motor is complete.

I need a battery for the outboard and having never had one with electric start I have no knowledge on the topic. So here come the questions:

1) what are the differences between marine and automotive battery? Can I use an automotive battery?
2) What size should I buy?
3) How many Cranking Amps should I be looking at?
4) should I get a deep cycle/cranking battery hybrid? Pure deep cycle not necessary as I will not be using a trolling motor or anything with an extended draw or a high draw (just lights, starting and horn as far as I can see).
5) I will likely buy the battery at walmart. no preference for walmart but in northern ontario there is on in everyone town of any half decent size. A swap would be easy if necessary. Anyone with battery experiences purchased at walmart?


One other question. What level of gas should I be using? Highest octane or is the blended gas ok?

Thanks in adavnce

Rob

 

[mfkadz]

A marine cranking battery would be best. You can get a smaller one if you like as you only have to turn the 40 over.

As for gas.... That's kinda like talking about religion, politics and life jackets. ;-)

mike

 

[Chris1956]

A series 24 marine battery is standard for that motor. A lot of those motors don't have any charging system. If your motor has no charging system, I would consider a marine starting/deep cycle combo battery.

 

[mfkadz]

A series 24 marine battery is standard for that motor. A lot of those motors don't have any charging system. If your motor has no charging system, I would consider a marine starting/deep cycle combo battery.

Just for my edification. Why a combo battery???

mike

 

[grumpyguy]

Thanks Mike and Chris,

I can understand the combo battery if there is no charging system. It is electric start so I would assume that the engine would charge the battery when running. It would seem idiotic to have a motor with electric start that didn't charge the battery. Pretty much kills and convenience gain if I have to charge the thing after every use OR if it dies from use while on a lake

How do I know if it does or doesn't charge? It only has the starter motor (no generator)

 

[mfkadz]

I did a little search in this forum and I am seeing it has no charging ability. The coils and magnets under the fly wheel make just enough power to run the motor once it's started.

I bet a cranking battery charge would last for a good bit before needing charging. You can extend that time with a bigger battery.

mike

 

[F_R]

Thanks Mike and Chris,

I can understand the combo battery if there is no charging system. It is electric start so I would assume that the engine would charge the battery when running. It would seem idiotic to have a motor with electric start that didn't charge the battery. Pretty much kills and convenience gain if I have to charge the thing after every use OR if it dies from use while on a lake

How do I know if it does or doesn't charge? It only has the starter motor (no generator)

That motor left the factory with no generator. A generator kit was offered as an accessory, however the great majority of motors never got one. If there is one, it sits opposite the starter motor and is driven by a notched belt. Not really idiotic, as that was pretty much the norm in those days. The battery is only used for starting, plus whatever other stuff you have hung on it such as lights, high powered radio, etc. A fully charged battery will give a whole bunch of starts. And if worse comes to worse, it can be hand started with the recoil starter.

 

[grumpyguy]

Thanks for the help everyone. I think I am going to buy a dual purpose starting/deep cycle battery to cover my bases.

 

[Vic.S]

Dual purpose batteries are usually just slightly modified starter batteries. that are suitable for limited deep cycling. Maybe a good choice for you., maybe no big advantage over an automotive starter battery.

However no battery should be left in a discharged or partially discharged state for longer than necessary. Recharge it as soon as possible when returning to dock. If that means taking it off the boat and transporting it home you will not be wanting one larger than necessary.
Is a solar panel a possibility?

And no you do not need a high octane fuel for a two stroke engine. Regular should be quite adequate

 

[grumpyguy]

Dual purpose batteries are usually just slightly modified starter batteries. that are suitable for limited deep cycling. Maybe a good choice for you., maybe no big advantage over an automotive starter battery.

However no battery should be left in a discharged or partially discharged state for longer than necessary. Recharge it as soon as possible when returning to dock. If that means taking it off the boat and transporting it home you will not be wanting one larger than necessary.
Is a solar panel a possibility?

And no you do not need a high octane fuel for a two stroke engine. Regular should be quite adequate

Yes I have a solar panel already. Only 5.5w but hopefully with the battery only responsible for the starting, the panel will be enough to keep me going for a week long fishing trip. No other electrical items will be on this boat other than the lights

Thanks Vic

 

[Vic.S]

Yes I have a solar panel already. Only 5.5w but hopefully with the battery only responsible for the starting, the panel will be enough to keep me going for a week long fishing trip. No other electrical items will be on this boat other than the lights

Thanks Vic

A quick back of envelope calculation suggests that a 5.5 watt panel should recharge the battery within an hour after starting So provided you don't keep stopping and starting or using the lights a lot. LED lights can help enormously in saving battery power.

 

[SparkieBoat]

I would be curious to know what your compression is. I know a lot of those older motors were very high compression 140+. Because the gas had much higher octane levels back then. I usually run 93 octane with anything over 130 PSI compression, but that is just me and I am all about safe guards. I think those motors also need 40:1 2 cycle oil. maybe 32:1, I am not sure. Chris or FR would know. good luck

 

[Chris1956]

OMC recommended a 24::1 gas/oil ratio for motors prior to 1964. However, some motors in 1963 were suitable to run 50::1 as they were all roller and needle bearings, rather than the older sleeve bearings. If Joe Reeves has not retired, he may answer the question, as he likely has specific knowledge about your motor.

FWIW, a 5.5Watt solar panel will create 55Watts of power in 10 hours of direct sunlight. There will be some loss in the electronics that convert that to 12DC. 55Watts is just over 4 Amps of power for your battery to recharge. I therefore would not expect very much charging of your battery, if any. A trickle charge is nominally .5A. So that solar panel (with 10 hours full sun) will be a trickle charge for your battery for 8 hours...and that is not much.

The good news is that a fully charged battery will last you a couple of weeks of normal use, before it needs recharging. Also, your motor should pull start quite easily, if the battery is weak.

 

[SparkieBoat]

pick up a cheap trickle charger from habor frieght, or one that has a 2 amp charger selector. the slow charge is the best charge.

 

[Vic.S]

FWIW, a 5.5Watt solar panel will create 55Watts of power in 10 hours of direct sunlight. There will be some loss in the electronics that convert that to 12DC. 55Watts is just over 4 Amps of power for your battery to recharge. I therefore would not expect very much charging of your battery, if any. A trickle charge is nominally .5A. So that solar panel (with 10 hours full sun) will be a trickle charge for your battery for 8 hours...and that is not much.

.

You seem very confused about all this.

A 5.5 watt solar panel has a maximum output power (P[SUB]MAX[/SUB]) of 5.5 watts That 5.5 watts irrespective of any timescale. The terminal volts at P[SUB]MAX[/SUB], will probably be in the region of 16 or 17 volts but should be quoted in the specs for the panel. This means that the current at P[SUB]MAX[/SUB] will be around 0.33 amps.. The maximum current, under short circuit conditions (I[SUB]SC[/SUB]) will be a little higher but at battery charging voltage is unlikely to be more than about 0.35 amps. Equivalent to a fairly low trickle charge current but potentially able to produce 0.35 Ah of charge in an hour or 2.8 Ah in 8 hours

A solar panel produces DC so there are no electronics, and therefore no losses in converting its output to DC.

If you assume that the OP's engine will take a current of 100amps when cranking and that it will hopefully start within say 5 seconds the Ah taken from the battery per start is 100 x 5 / 3600 = about 0.14 Ah. Hence my earlier suggestion that the battery should be recharged by the solar panel within an hour.