How many batteries on a small boat?

Johnny Sixgun

Go where the fleet isn't
Sep 7, 2014
210
110
43
51
N32.45 W117
Name
John
Boat
TTT
Have a small 15' boat with a Evinrude 70 on it. Only electronics on it is bait pump, bilge pump and VHF radio. Do I need a separate battery for them or will one battery suffice for all?
 

Arima-bob

Ship faced aquaholic
Mar 9, 2012
4,342
2,812
113
Too far from water
Name
Beeulzebob
Boat
uh....
One would probably be fine, but two is better. Sucks being on the water with a dead battery.
 

ssrmr2

Well-Known "Member"
Mar 15, 2006
689
266
63
41
Cypress
Name
STEVE
Boat
17' montauk "Anger Management"
I run 2 one dedicated for the trolling motor and everything else of the main. there is a combine feature and a charging relay as the posts above shows
 

hucklongfin

Deep release specialist
Jul 3, 2003
8,104
5,076
113
63
Mission Viejo
Name
MarkT
Boat
Blazer Bay 1860
I run 4, 2 for the 24v trolling motor and 2 12v on a switch for starting/house.
 
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Hellosugaree

Newbie
Sep 6, 2019
95
75
18
35
San Francisco
Name
Timbo
Boat
13' Boston Whaler
I toyed with this idea few weeks ago for a 13ft boat.

I almost convinced myself to get 2 batteries, but to do it right you need a VSR or other way to isolate the starting battery from the accessories while still allowing the motor to charge the second battery after the starting battery is full. Too much crap to fit in a boat that's already too small.

I ended up just getting the biggest dual purpose battery I could fit under the seat. Small pump and fishfinder don't eat that much juice and I'm not running them for 10 hours straight with the motor off anyway.
 

gunnyslinger

I've posted enough I should edit this section
Mar 15, 2006
1,031
612
113
Huntington Beach
Name
Justin
Boat
20’ CC
4 total on my 20’
2 are for 24v TM
I’ll never go out with less than 2 after a dead battery on the water.
 

tuner

pysgotwyr
May 24, 2006
1,231
722
113
Huntington Beach
Name
Steve
Boat
260 Mackinaw
Run 1 lead acid that will handle the starting load from the 70 and bring along a small Li-Iron jumper pack for back-up. I would consider a good quality AGM for the main battery (not Optima). I run a small SLA in my 12' Klamath to save weight but still handle starting the 20hp Tohatsu and run a small MFD. Worst case, I can pull start, not sure that is an option for you.
 

MYNomad

Heading South
Dec 12, 2007
3,200
2,687
113
Pacific Northwest / West Coast Mexico
Name
Rick
Boat
Yes
Here is an idea that works great for me and my 14' dinghy, which was born with only one battery and would be difficult to install a second. But, when my battery crapped out and left my stranded (60 hp 4 stoke outboard which really can't be pull started), I bought a new battery. Then that one crapped out. This is the good part -- that's when I bought one of the new generation jumpers -- very light, lots of capacity, and hold a charge a LONG time. Now if my battery every dies again (the dinghy doesn't get enough use to keep the battery healthy without charging between uses, which I have been too lazy to do), I can easily jump start.

This is the one I purchased -- different sizes are available (I was even considering buying one for the big boat, but the biggest will start only a 6 liter diesel, and mine are 11 liters; Then it occurred to me, the one I have for the dinghy (and if I am on the big boat, so is the dinghy) is adequate to start a genset.):
Amazon product
 
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Hellosugaree

Newbie
Sep 6, 2019
95
75
18
35
San Francisco
Name
Timbo
Boat
13' Boston Whaler
Two replies saying "4 batteries" It's a 15' boat guys with no mention of a trolling motor.
I never go out with less than 15 batteries. 3 starting batteries for redundancy, a 5 battery house bank to run the 7 inch fishfinder, 4 lithium batteries for the trolling motor, and a 3 battery bank for the bilge pump. Plus I always carry 2 spare battery starters just in case. When my boat starts sinking due to being overweight from 800lbs of batteries, at least I know ill be able to start the motor for sure.

A good safe but not overly conservative rule of thumb is 1 battery per foot of hull length.
 
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pacificscout

Hey! You got any frozen ice?
Jul 28, 2012
2,417
1,580
113
Fullerton
Name
Wally
Boat
16ft Scout EMBUSTERO
Boat motor battery was wired for it and the bait tank.
I got a lawnmower 12v that is for my fishfinder.
I used it once to help other boater's dead battery.
Charge it before going out.
 

beerman1

Member
Jul 14, 2014
131
136
43
OC
Name
eric
Boat
triumph 17 CC
I run everything of my lead acid marine battery but always have a spare blue top Optima . Only needed it once when my old juicer expired, but was damn glad I had it. Just takes me a minute to swap them.
 
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gunnyslinger

I've posted enough I should edit this section
Mar 15, 2006
1,031
612
113
Huntington Beach
Name
Justin
Boat
20’ CC
Two replies saying "4 batteries" It's a 15' boat guys with no mention of a trolling motor.
Anyone with a brain can come to the conclusion that 2 batteries were recommended. Simply mentioned 2 were for the TM’s.
 

Croaker.Stroker

Old White Guy
Nov 28, 2015
1,184
914
113
Tustin
Name
Croaker
Boat
Arima Sea Pacer
I have three on my 17’. One is dedicated to the MFD. One runs the bait pump. One starts the motor.
 

MATTANZA

old man of the sea, in training.
Aug 23, 2004
4,744
1,895
113
SAN DIEGO
Name
RICK
Boat
Boston Whaler 25' Outrage "MATTANZA II", 34' Radovcich "AMY ANNE" {when it needs to be fixed}
if your engine will pull start , you only need one, but 2 is always better, i'd get a group 30 size. 2 is a little over kill or 2 group 24's. my 15 aluminum skiff only had 1 24 size battery, bait tank, radio , and fish finder. I never had any trouble.