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Discussion Starter · #1 ·
i have a deep cycle battery that i have for my trolling motor, fish finder, lights and horn but do i also need another cranking battery for the johnson javelin 85 hp motor i just got?

i am about to run all the cables and i need to know.
 

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I would recommend an additional cranking battery. Mainly because the trolling motor is likely drain the battery to the point that it won't crank the engine. Also, I would suggest connecting the other electronics to the cranking battery and reserving the deep cycle for the trolling motor. The problem with having the fishfinder on the same battery as the trolling motor, is that the trolling motor can interfer with your fishfinder readings.
 

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If you have room for two... I would recommend a 2nd battery if storage and weight arent an issue.
Always good if you can isolate or have at least a 3 way position switch to be able to run off batt 1 and have batt 2 as a back up.
 

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Discussion Starter · #4 ·
but would i need a second 2 cycle battery or is a cranking battery a different type?

and ive seen those switches but is it ok to wire them together like that? doesnt it up the voltage? would that hurt my trolling motor etc?
 

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I now have a combination start/troll deep cycle battery I use full time for trolling motor and depth finder and I have a cheapy 550cold cranking amp start battery for the motor. In a pinch one or the other should have the charge I need to get home. I have them wired seperately so they dont draw or effect one another and the motor only charges the starter battery. I recharge the other at home and keep a trickle charger on both at home.
 

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All the switch does is select either battery 1 only, or, battery 2 only, or COMBINE for emergency starting if one battery isnt enough to crank over the motor.

Yes, cranking batt's are very different from Deep Cycles. Basically, cranking batt's put out alot of amps for a very short amount of time (ie. starting motor's - just like the batt you have in your car/truck).

A deep cycle puts out X amount over a longer period (i.e. running electronics, trolling motor, lights).

A cranking battery doesnt recover well from a deep discharge, whereas a deep cycle battery can take deep drains and can be charged back up numerous times.

Physical differences are deep cycle batt's have thicker plates (hence can accept repeated rechargings better) and are considerably heavier than cranking batt's.

Cranking batt's are a little lighter than deep cycles and dont handle deep discharges very well as they have thinner plates internally.

Both put out 12 volts, and there are many flavors in battery amperages, reserve cranking amps, amp hours.

Usually, a group 27 cranking battery will pretty much be the best bet for a motor starting battery.

A group 24 or group 27 would be good to run simple electronics and systems.
For heavy draw for items such as trolling motors, at least 2 parralled group 27's would be a better bet.

For my boat I ran my electronics on deep cycle batt's only. I had high draw unit's, so in my case, one battery could do it for a day trip out... but probably no longer than that and would drain from use to almost half the battery capacity for the day.. so I ended up paralleling 3 group 27's at a rating of 140 amp hours each which gave me over 400+ amp hours of power.. this allowed me to run full electronics at full power for at least 3 days without depleting the batteries capacities below 50% (color plotter, color sonar, vhf, CD/radio player, deck lighting, and second sonar unit, not to mention charging cell phones and a power to a back up portable GPS).

I had 2 dedicated cranking batteries that started the motors.

That's only an example....

if you can rig 2 switchable batt's, I think you could have enough power for what you plan to do if day tripping. One group 27 deep cycle for running electronics and stuff while fishing, and one group 27 for motor starting
 

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Dave did a great job laying it out. There are also many good sites on the the web that talk about marine batteries like this one

I have one deep cycle and one cranking battery in my boat. I use a selector switch to determine which of the two or both I want connected to the engine. I use a dual charger (two separate outputs) to recharge them as they both have different recharge cycles (3 stage). Keep in mind, an outboard engine puts out very little excess current so it is a poor recharger. It will do okay in topping off your cranking battery under normal use but isn't effective in recharging a deep cycle battery that has been heavily used so go with a charger (either portable or one that is installed on your boat if you have the room (they are small).
 
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