Battery for 20hp Outboard on 10' RIB

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mvweebles

mvweebles

Guru
Joined
Mar 21, 2019
Messages
7,218
Location
United States
Vessel Name
Weebles
Vessel Make
1970 Willard 36 Trawler
I'm just getting around to final setup of the AB Aluminum 10'6" RIB with Tohatsu 20hp (with electric start/tilt). Looking for ideas on battery selection, placement, and protection. My model of RIB does have the bow-box (also aluminum), though the cables on the OB would need to be extended. With 3-gal fuel, not a ton of room in the bow box.

I came across this small form factor LiFePO4 battery for motorcycles by Antigravity. Never heard of them, but they are US-based and appear to cater to motorcycle custom/race segment where size and weight are important (2.5lbs in 6" x 3.5" x 3.5" case).

https://antigravitybatteries.com/products/starter-batteries/restart-oem/atz10-rs/

QUESTIONS:

1. LifePO4 for starter on 20hp? Guessing same as the small start-packs that I see at stores. Claims 360 CA (cranking amps).

2. Where to mount? I could mount forward in the bow-storage, but that would limit me to a 3-gal tank. Plus cables would need extending. Given the small size of the battery, was thinking attaching to inside of transom.....but that's hardly a dry spot. Maybe an enclosure such as a waterproof junction box such as THIS ONE? Maybe with a vapor-tight thimble to run the cables?

Thanks in advance -

Peter

AB Bow Locker.jpg

AB 10.jpg
 
Looks semi-good on paper, I think.

Note this:

Use only Lithium specific Motorsport Chargers to charge this battery! Do not use Lead/Acid Chargers.​

Maybe hang a battery box from the top of the transom? Off to one side of the mount clamps?

-Chris
 
Definitely not in the bow with the gas tank. I like the stern mount in the box. It’s a short run to the starter. I am waiting for my current RIB battery to give up and switch to an LFP motor cycle battery.

Tom
 
Depending on your davit system you may need a battery which can be tipped or inverted.

pete
 
Pete Meisinger said:
Depending on your davit system you may need a battery which can be tipped or inverted.

pete
Click to expand...

The LiFePO4 batteries can be mounted in any orientation.

I'm also struggling to size the battery. The link I included above is for a 360 CA battery and is used in pretty large motorcycles ("Up to 1000cc's"). The smaller sister battery (HERE) is also spec'd for 1000cc motorcycles but is only rated by OEM at 180 CA. Tohatsu manual states the 20hp needs 330 CCA (yes, traditional CCA vs "CA" used by LFP OEMs), but that's for a wet-acid battery. Now, I realize amps-are-amps, but if these small batteries (and their start-pack cousins) are starting large motorcycles and small cars, you'd think it could start a 20hp outboard. Wish I knew for sure (I've sent an email to Antigravity, but I'm guessing they'll give a wishy-washy answer).

The small 180CA battery would be really easy to find an enclosure for - standard sized junction boxes available. The larger 360CA battery would be more challenging.

Peter
 
Last edited:
A lead acid battery charger like the OEM Tohatsu’s will work, but it will only charge a Li battery to 70% SOC. But that should be ok for a starting battery and 70% should give better life.

Do make sure that the starting current doesn’t exceed the Li battery’s max amp rating.

David
 
I have been using lawn tractor batteries for years in my avon with remote steering for years. The batteries are around $45 at the local box hardware stores. I typically get 4 years on a battery. I think it would last longer if I treated it better. It often gets forgotten at the end of the season and it gets the crap beaten out of it in the rough riding inflatable.
Hollywood
 
hollywood8118 said:
I have been using lawn tractor batteries for years in my avon with remote steering for years. The batteries are around $45 at the local box hardware stores. I typically get 4 years on a battery. I think it would last longer if I treated it better. It often gets forgotten at the end of the season and it gets the crap beaten out of it in the rough riding inflatable.
Hollywood
Click to expand...

Similar experience with my Honda 40. My small (same size as in my lawnmower) AGM will lie on its side if you have SeaWise or Weavers. I have had to charge mine a couple of times, as it gets ignored most of its life, including a 6 month or longer layup in the winter. More than 4 years life. I think I am on my second, don't know how old the first was when I bought this dinghy 12 yrs ago.
 
koliver said:
Similar experience with my Honda 40. My small (same size as in my lawnmower) AGM will lie on its side if you have SeaWise or Weavers. I have had to charge mine a couple of times, as it gets ignored most of its life, including a 6 month or longer layup in the winter. More than 4 years life. I think I am on my second, don't know how old the first was when I bought this dinghy 12 yrs ago.
Click to expand...

My thinking is Lithium battery will do much better during long periods between use. I've read where FLA have 3%/mo of self-discharge; AGMs are a little better. LFP are essentially 0% self-discharge.

I wish I could figure out what size batter is needed. The Tohatsu recommendation of 330 CCA seems awfully high compared to what motorcycles are running via LFP.

Thanks for all the input - very helpful for me.

Peter
 
mvweebles said:
I wish I could figure out what size batter is needed. The Tohatsu recommendation of 330 CCA seems awfully high compared to what motorcycles are running via LFP.
Click to expand...


We have the Suzuki DF20A, electric start and power trim (or tilt or something)... and the manual calls for 450 MCA or 330 CCA or 70 RC. Which sounds pretty close to yours...

Our dinghy receipt indicates Deka 11U1L. Lookup suggests "Outdoorsman" sealed/flooded, 350 CCA, 410 MCA. Works OK, but this will be our first winter with it.

I had asked for AGM, but that apparently got lost in the shuffle. Maintenance free/sealed (and gel) not recommended by outboard manual because might not be compatible with Suzuki charging system.

We've had decent luck with our various AGMs not self-discharging over our 3-month (-ish) winter layups -- with no interim charging at all.

If you bag the lithium idea, you might look at an Odyssey ODS-AGM28 in their powersport line -- several versions, different terminal configurations -- which looks to be smaller but slightly heaver than our Deka 11U1L.

-Chris
 
Last edited:
mvweebles said:
That battery is listed as 150 CCA. I would think that's fine for a smallish outboard, but less than half thr Tohatsu recommended 330 CCA. Did I read the description correctly?

Thanks

Peter
Click to expand...
Peter, that size is recommended for Harleys among other 2 cylinder engines. Ought to be ok for 330cc.
I think their CCA numbers are very conservative. They list 400 cranking amps, too.
Also, I think I bought the PC680 after looking at the PC545. Not entirely sure, as it has been a while.
No problem starting my very similar 18hp Tohatsu and check out the mounting brackets. Mine sits attached near the transom and does ok.
 
Last edited:
Hi Peter,

We installed an Earth-X battery with our Tohatsu 20 almost 2 years ago. So far so good. It sits for months at a time (but not for much longer!) and we have never attached a charger.

https://earthxbatteries.com/product/etx680c/

Best Wishes
 
Nice looking rig. I just bought a new EFI 25 yamaha and barely see a. Voltage drop at the battery when cranking and with EFi it starts right up. So i think it would work just fine.

I would mount up front and. Utilize the run/chase for thee fuel with as big a set of cables that would fit. Weight up front always helps the ride and can help balance out any davit lift. (My 25hp with trim tilt start is about 130lbs.)

You can either bolt or weld it on the bulkhead to front tank and punch a hole in the bulkhead to run cables into the chase. Would be nice to simply extend the front seat over the bulkhead and mount it underneath.
 
I have been using a group U1 battery for starting a 25hp Ev Evenrude ETEC. The AGM battery is rated a 225 cca. Works great. I switched from a group 27 to the U1 to save about 25 lbs to help reduce boat weight. If you have electronic’s that you might leave on without the engine running a larger battery maybe A better choice
 
I put together a set-up like you described a couple of years ago. My new dinghy had a 15hp Tohatsu.
I went with an Antigravity AG-1201 battery https://antigravitybatteries.com/products/starter-batteries/small-case/ag-1201/.
I bought this charger for it from Amazon. https://www.amazon.com/gp/product/B0167JU8VI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I put the battery in this Pelican case which fit great https://www.amazon.com/gp/product/B0014D47RY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
And I added a quick disconnect so the battery could be easily removed https://www.amazon.com/gp/product/B00QI6S68S/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The setup was super lightweight, plenty powerful and worked great.
 
Woodstock said:
I put together a set-up like you described a couple of years ago. My new dinghy had a 15hp Tohatsu.

I went with an Antigravity AG-1201 battery https://antigravitybatteries.com/products/starter-batteries/small-case/ag-1201/.

I bought this charger for it from Amazon. https://www.amazon.com/gp/product/B0167JU8VI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I put the battery in this Pelican case which fit great https://www.amazon.com/gp/product/B0014D47RY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

And I added a quick disconnect so the battery could be easily removed https://www.amazon.com/gp/product/B00QI6S68S/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1



The setup was super lightweight, plenty powerful and worked great.
Click to expand...
I actually offered that battery but canceled because it does not have a BMS. I have no idea if one is needed in this application, so I decided to order one with a BMS.

Good tip on pelican case.

Peter
 
mvweebles said:
I actually offered that battery but canceled because it does not have a BMS. I have no idea if one is needed in this application, so I decided to order one with a BMS.

Good tip on pelican case.

Peter
Click to expand...

This picture is of the finished install.
 

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mvweebles said:
I'm just getting around to final setup of the AB Aluminum 10'6" RIB with Tohatsu 20hp (with electric start/tilt). Looking for ideas on battery selection, placement, and protection. My model of RIB does have the bow-box (also aluminum), though the cables on the OB would need to be extended. With 3-gal fuel, not a ton of room in the bow box.

I came across this small form factor LiFePO4 battery for motorcycles by Antigravity. Never heard of them, but they are US-based and appear to cater to motorcycle custom/race segment where size and weight are important (2.5lbs in 6" x 3.5" x 3.5" case).

https://antigravitybatteries.com/products/starter-batteries/restart-oem/atz10-rs/

QUESTIONS:

1. LifePO4 for starter on 20hp? Guessing same as the small start-packs that I see at stores. Claims 360 CA (cranking amps).

2. Where to mount? I could mount forward in the bow-storage, but that would limit me to a 3-gal tank. Plus cables would need extending. Given the small size of the battery, was thinking attaching to inside of transom.....but that's hardly a dry spot. Maybe an enclosure such as a waterproof junction box such as THIS ONE? Maybe with a vapor-tight thimble to run the cables?

Thanks in advance -

Peter

View attachment 134201

View attachment 134202
Click to expand...

If you missed the comment - DO NOT PLACE BATTERY IN FUEL COMPARTMENT! Explosion hazard. Mine is on the transom.
 
Caballero II said:
If you missed the comment - DO NOT PLACE BATTERY IN FUEL COMPARTMENT! Explosion hazard. Mine is on the transom.
Click to expand...


I did not miss your comment. Frankly, I'm surprised I didn't think of it because the explosion risk is extreme so I really appreciate your noting what should have been obvious to me (it wasn't).

Based on previous comment about Pelican Case, I am going to try a waterproof junction box mounted on the outside of the bow-locker wall, more or less facing the engine but in forward part of RIB. I found this waterproof junction box as the Pelican Case was a bit small for the battery I chose. The Tohatsu battery cables are long enough to go beneath the false-floor and mount in the new box.

I'll post an update in a week or so when I get everything sorted. Many thanks to all -

Peter
 
Just finished the same project for a 11 ft RIB with double floor, 20 hp Honda. Fitted a bow tank in the storage area. The battery is a tractor battery purchased at NAPA. Should get 4 years. Installed it in a battery box that is strapped to the stainless steel hardware. Also added a small water separator to the transom ahead of the engine intake.

71BMtOV5qfL._AC_UL320_.jpg
 
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