Two deep cycle / starting combo batteries wired in parallel instead of...

[Racklefrack]

I have a small 18' bowrider with minimal power needs -- standard stereo, VHF radio, charge phones and tablets once in a while, and -- of course -- starting the boat. I'm strongly considering swapping out my single starting battery for two deep cycle / starting combo batteries wired in parallel. My motor only needs 375 CCA's if memory serves, and a single deep cycle / starting combo battery has like 500 CCA's so two wired in parallel should be more than enough. Plus, with roughly 75Ah's of reserve x2 I could easily run my electronics without worrying about being able to start the boat at the end of the day.

I know it's popular to separate the batteries using a selector switch, but for my little boat with so little draw I just don't see the point. Two batteries wired in parallel to serve both starting and accessory needs sounds like the perfect solution.

Thoughts?

 

[alldodge]

If you can start the motor with a pull cord in an emergency, go for it

Another option which a fellow iboater did, was use a lawn mower bat to start his with and did just fine. Its light and doesn't take up much room, but would suggest trying it first before switching

 

[dingbat]

I have a small 18' bowrider with minimal power needs -- standard stereo, VHF radio, charge phones and tablets once in a while, and -- of course -- starting the boat. I'm strongly considering swapping out my single starting battery for two deep cycle / starting combo batteries wired in parallel. My motor only needs 375 CCA's if memory serves, and a single deep cycle / starting combo battery has like 500 CCA's so two wired in parallel should be more than enough. Plus, with roughly 75Ah's of reserve x2 I could easily run my electronics without worrying about being able to start the boat at the end of the day.

I know it's popular to separate the batteries using a selector switch, but for my little boat with so little draw I just don't see the point. Two batteries wired in parallel to serve both starting and accessory needs sounds like the perfect solution.

Thoughts?

Why bother installing two batteries when a larger, single battery will supply the same current?


Batteries will equalize should something go wrong with one of the other. Instead of one bad, isolated battery, you now have two dead batteries which totally defeats the purpose of the second battery

 

[Racklefrack]

"Why bother installing two batteries when a larger, single battery will supply the same current?"

One single battery can't supply the amp hour reserves of two batteries wired in parallel. That reserve power is what I want to accomplish since it would virtually eliminate the risk of killing a battery by running the stereo all day.

"Batteries will equalize should something go wrong with one of the other. Instead of one bad, isolated battery, you now have two dead batteries which totally defeats the purpose of the second battery."

Batteries equalize, that's true, but the chances of something going wrong with one of them on any particular day trip are infinitesimal, so unless I install them and then ignore them for years -- which isn't likely -- then I'd have plenty of advanced notice that something might be wrong with one of them just through routine inspection and maintenance.

 

[Racklefrack]

"If you can start the motor with a pull cord in an emergency, go for it."

Pull-starting a 4.3 MPI... I'll look into that.

"Another option which a fellow iboater did, was use a lawn mower bat to start his with and did just fine. Its light and doesn't take up much room, but would suggest trying it first before switching."

If you're suggesting I use a lawn motor battery as a backup for the two combo batteries wired in parallel in case it doesn't work, then I think I'd prefer to use a jump starter pack instead.

 

[Chris1956]

Gee, if you have all the answers, why ask us?

A single series 27 battery will be more power than you will need. If you want 2 batteries, spend the extra $ and get a battery switch.

You are not pull starting a V6. Alternatively, stick with a single 24 series battery and take out a towing policy.

 

[alldodge]

"If you can start the motor with a pull cord in an emergency, go for it."

Pull-starting a 4.3 MPI... I'll look into that.

"Another option which a fellow iboater did, was use a lawn mower bat to start his with and did just fine. Its light and doesn't take up much room, but would suggest trying it first before switching."

If you're suggesting I use a lawn motor battery as a backup for the two combo batteries wired in parallel in case it doesn't work, then I think I'd prefer to use a jump starter pack instead.

MY thought was you had a little motor "You did not say"

If you would have said what motor, my comment would have been different
Sorry for my comments, you got it figured out

 

[Racklefrack]

"Gee, if you have all the answers, why ask us?"

Because I don't have all the answers. For instance: No one has been able to adequately explain why separating two batteries with a switch is preferable to simply wiring them in parallel for something as general purpose as I described. A switch has to be installed, then switched to the correct position, then switched back and so on; two batteries wired in parallel supply ample power for starting AND accessories without ever having to even open the engine cover. It just sounds a lot simpler to me.

It's a common practice in RV's that have significantly higher power needs than my boat, so the answers I don't have is 1) Why NOT run two batts in parallel and 2) Why is a switch better?

"Alternatively, stick with a single 24 series battery and take out a towing policy."

I have a tow policy, I simply prefer to avoid using it if the simple installation of a second battery could virtually eliminate the risk of killing a single battery during a normal day's use.

 

[Racklefrack]

MY thought was you had a little motor "You did not say"

If you would have said what motor, my comment would have been different
Sorry for my comments, you got it figured out

And I apologize for not being clearer; I absentmindedly assumed the description of my power needs was enough info.

 

[dingbat]

i have a tow policy, I simply prefer to avoid using it if the simple installation of a second battery could virtually eliminate the risk of killing a single battery during a normal day's use.

You're not adding a second battery. Your creating a larger, single battery.

No redundancy. No protection whatsoever from discharging your “single” battery below the needs of the starter. Play your stereo too long, your done. Call SeaTow.

Batteries have a very high failure rate. Don’t give a darn if you maintain them or not. They fail when they fail. You have no control over it

Im an offshore guy. 90 miles off the coast isn’t a place you want a battery failure. As such, I have batteries and navigation scheme to minimize the effects of a power failure.

I run two batteries isolated from each other and charged with an ACR. The house load has no affect on my ability to start the motor and a failure of either battery can’t take down the other. I turn the switch On in the morning. Turn the switch off at night.

Should something happen to the primary battery, I have the ability, through the switch, to connect either or both batteries to the starter

Primary navigation (GPS1), communications (VHF1) and motor on battery 1.

Back up navigation (GPS2) communications (VHF2) sonar, radar and house load is on battery 2.

Unless both batteries fail at the same time, Im coming home. You can’t say that with your parallel scheme.

 

[Racklefrack]

Unless both batteries fail at the same time, Im coming home. You can’t say that with your parallel scheme.

I appreciate your input. Fair winds and following seas to you, sir.