Thread Tools Search this Thread Display Modes
Old 03-09-2019, 11:02 AM   #1
Senior Member
Tator's Avatar
City: Bainbridge Island/Petersburg Alaska
Country: United States
Vessel Name: Oz
Vessel Model: Bluewater 40' RPH 1979
Join Date: Feb 2015
Posts: 203
battery for dinghy out board

I'm trying to make a little more room in the inflatable and would like to downsize the starting battery. I currently use an identical battery to the one I use to start my Onan 7.5MDJE. It's 900 miles away and I can't remember if it's a 24, 27 or larger. The motor is an 18hp Tohatsu w/elec. start. The manual calls for a group 24 which seems like overkill. I was wondering why one couldn't use a motorcycle battery or one like the one in my home gas genset. I'm looking at ones that have between 240-275 CCA. What do you all use and any other thoughts?


Tator is offline   Reply With Quote
Old 03-09-2019, 11:13 AM   #2
City: San Francisco
Country: USA
Join Date: Apr 2018
Posts: 1,164
150 hp motorcycles are started by 15 AH batteries. If you want to go really small and light, use an LFP designed for motorcycle starting.

DDW is offline   Reply With Quote
Old 03-09-2019, 11:27 AM   #3
ranger42c's Avatar
City: Maryland
Country: USA
Vessel Model: 42' Sportfish
Join Date: Aug 2013
Posts: 5,016
I got a small AGM "sports power" battery for our outboard. Deka ETX30, I think. The outboard is a Suzuki DF15A (15-hp, same basic platform as their current 9.9 and 20-hp models).

Started with the outboard manual, found minimum cranking amp recommendation, went from there. AGM to mitigate self-discharge over winters (I could periodically recharge, but have found that not necessary with AGMs).

South River, Chesapeake Bay
ranger42c is offline   Reply With Quote
Old 03-09-2019, 12:06 PM   #4
Technical Guru
Ski in NC's Avatar
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 5,651
Check the charging volts with engine running at say 2000rpm, and with battery fully topped up prior to starting. See what voltage plateaus at. Some of these little motors have very crude voltage regulation (volts go over 14.5, maybe a good bit over) and a bigger batt can tolerate that better than a little one.
Ski in NC is online now   Reply With Quote
Old 03-09-2019, 12:19 PM   #5
TF Site Team
FlyWright's Avatar
City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 12,719
Take a look at this Odyssey AGM battery. We used them in my job for mobile power needs. Small, dense and powerful.

roughly 10"x6"x4", 20 lbs with a 400 CCA rating.
My boat is my ark. It's my mobile treehouse and my floating fishing cabin. It's my retreat and my respite. Everyday I thank God I have a boat! -Al

@DeltaBridges - 25 Delta Bridges in 25 Days
FlyWright is offline   Reply With Quote
Old 03-10-2019, 10:23 AM   #6
kchace's Avatar
City: Brookline, NH
Country: USA
Vessel Name: Blue Heaven
Vessel Model: Albin 43 classic double cabin, twin 135 Lehmans
Join Date: Sep 2013
Posts: 1,807
I bought a U1 size Lawn Tractor battery from Walmart for $20 4 years ago. Put it in a small battery box (available on Amazon) and its been starting our Tohatsu 9.8 great. Granted it is a standard Lead Acid battery, so it can't be tipped on its side, but if you aren't going to do that then its all you need.

kchace is offline   Reply With Quote
Old 03-10-2019, 11:39 AM   #7
City: Fairport, NY and Palm Coast, FL
Country: United States
Join Date: Jan 2017
Posts: 1,869
I'd pitch the starter motor and battery. save 60 lbs or so. But, that's just me.

diver dave is offline   Reply With Quote
Old 03-10-2019, 12:05 PM   #8
Senior Member
Rain Dog's Avatar
City: Pensacola, FL
Country: United States
Vessel Name: Rain Dog
Vessel Model: Grand Banks 42 Classic
Join Date: Feb 2016
Posts: 184
I use an Odyssey PC625. Great battery. Small, light, and stands up to years of abuse it gets on the floor of my dinghy.

Rain Dog is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 04:05 PM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012