Do I need a battery for an Electric start outboard?

[Frankly]

The English part of my Tohatsu OM only goes up to page 86 (covers 9.9, 15, 20 HP). Maybe my original premise is in error. Mercs may not be same as Tohatsu or maybe mfg just figured this out. I will make a point to keep the battery switch on.

I have cranked it a couple of times by hand (with no battery). Do have to pull it a couple of times which I assume is to charge things enough to power the EFI system. On battery it busts right off.

Reading all the warnings (BS and real). They mention manually pulling it through to prime the oil system after long periods of non use.


Bottom line RTFM.


Frankly


From Mercury: motors 30 HP and less are built by Tohatsu. Built by not same as or identical to.

FWIW
Nissan outboard motors are produced by Tohatsu Corporation of Tokyo, Japan. ... Mercury outboards from 30 hp and below are rebadged Tohatsus and all Nissan outboard engines in the US and Canada are Tohatsu's with a Nissan decal.
Wikipedia › wiki › Nissan_Outboar...
Nissan Outboard Motors - Wikipedia

[boat driver]

Originally Posted by Wotname

Welcome aboard CF, Memelado.

You should be OK but check with the salesperson or get a copy of the operating manual.

I have never seen an alternator that can be harmed by operating with no battery (at start up) but there is always a first for everything. Conventional alternators do not self excite at start up so it should never try to output any current.

alternators should not be left without battery- unless field wire is disconnected so can not self excite.

The smaller outboards use a rectifier, and some may be damaged without a battery or load.
two ways of solving problem- find out what the amperage is and put a white stern light on cowling so creating load or simply remove rectifier until you want it. absolutely read instruction manual.

[Jim Cate]

Originally Posted by lvictorlucas

Use a super capacitor instead. It is very small and light while giving you the option to electric start or elect prime while protecting the alternator from voltage spikes while requiring no field winding switch and will work on any motor or alternator. It also provides a backup to charge your phone or run a 12V LED light.

Taking electrical advice from anyone named "Lucas" is dubious...

(Just joking, everyone!)

Jim

[a64pilot]

Originally Posted by boat driver

The smaller outboards use a rectifier, and some may be damaged without a battery or load.

I think it being a magneto system with a rectifier is the issue, I don’t believe they are alternators.
A magneto system with a rectifier is like older motorcycles were, they made as much current as they could, and any excess was shorted to ground via the rectifier, on those having a largish load was actually good for them as it was less power the rectifier had to short to ground and the less heat.

There are many, many LFP motorcycle batteries available that weigh next to nothing and I believe may even even be able to mount under the cowling. All that I’ve used are based on A123 cells and the size and power of the battery was based on number of cells.
I have a 4 cell in my Husqvarna TE-450, and it worked great for years. My CBR-1100XX had I think an 8 cell, still less than 2 lbs.

Attached link is just for reference, there are many others, 6 and 8 cell too, but I feel sure that a 4 cell would work.
Weight is 1 lb.
https://www.revzilla.com/motorcycle/...QaAj3sEALw_wcB

With one of these, you could electrically start it, and add 1 lb of weight to the motor if mounted under the cowling.

[Dave22q]

Logic says of course you do not need the battery. Caution says that unless the manual explicitly confirms this opinion, carry a battery. They are not that bulky.

[Frankly]

Keep in mind these are electronic fuel injected outboards (for the last couple of years). Mine will start and run without the battery (did that early on still deciding on battery arrangement). This would indicate some additional electrical load over just firing the spark plugs.

I think that motorcycle battery costs $25 over at Sam's and it and a Blue Sea small battery switch all comfortably fit in a plastic battery box. Think I did cut the box down a bit so it would slip under the Whaler seat.


Frankly

[Memelado]

Originally Posted by s/v Jedi

Y’all would be wrong and likely end up with a ruined system.

Questions like these do not belong here; the manual is the authoritative source of information, not the opinions of people on a forum

Here’s a $39 small battery that works great and can be stuffed anywhere: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

How would I connect the wires to this battery? The wires on the motor have ciruclar metal ends meant to slide onto the post of a marine battery. Do I have to somehow alter the wires?Thank you for finding that info in the manual by the way. I couldnt find it myself

[s/v Jedi]

Originally Posted by Memelado

How would I connect the wires to this battery? The wires on the motor have ciruclar metal ends meant to slide onto the post of a marine battery. Do I have to somehow alter the wires?Thank you for finding that info in the manual by the way. I couldnt find it myself

No problem, glad to help. The ring terminals from the engine fit straight to the battery terminals using the hardware that comes with the battery. You don’t need fuses, switches etc. (fuses already under the cowling)

This battery is the same as the $29 batteries at Good Sams, Costco etc. But you pay $10 extra for the shipping.

[gkunkle999]

Yes you need a battery. Smaller out boards DO NOT have alternators. As noted by others they use a rectifier. Running the engine with no battery will damage/blow the rectifier.
Also as noted above the engine blocks are the same, the carburation is the difference between the 9.9 and 15