Lead acid battery. Two questions

[redneck joe]

My current battery is use for starting and as my trolling motor backup is a 2018 deep cycle, not sure how many CCA but never had an issue and usually kicks in about 15 seconds and it came from my Carver with a 5.7 mercruiser as the starting battery.

First question is I've read one should not use a deep cycle for starting it will damage things. In a quick search my 50hp needs 500 or so CCA and a 115 (max rated hp) would need 750ish. As long as i get enough CCA on a deep cycle can I not enjoy the benefits of both?


Second question is the current set up is nine inches tall, plus connections so about 11.5 inches tall. Is there a battery that fills the above but is a couple inches shorter for where I want to place it?I looked at a battery group chart and was immediately overwhelmed.

I guess third questions is... could i relocate battery? How long of a run from battery back to the original location where I could put a bus bar or whatever it's called.

 

[Scott Danforth]

there are dual purpose batteries (starting and deep cycle). however generally starting batteries have thicker plates, deep cycle batteries have more thinner plates.

using a deep cycle as a cranking battery works until the cranking load overheats the plates and they warp, shorting out your battery.

what group number is your current battery?

look here for dimensions. https://batterycouncil.org/wp-content/uploads/2023/10/BCI-Group-Sizes.pdf

where would you want to move the batteries? I would probably install under the console

 

[redneck joe]

Group 31 pretty sure from dimension.

Three poss loations possible locations roughly 6, 9, or 16ft of wire away from the stern where it is located now. Most likely would be the 6 (under helm) or 9 in a new space in front of the fishbox which is in front of the helm.

 

[redneck joe]

Ok looks like any side post unit fixes my problem. I (will) have lifepo up front next year for my trolling motor but also want the rear as a backup to act as a kicker if both main motor is out and lifepo gets drained. That is why I was thinking deep cycle. If I go non deep cycle what could I expect for performance of a deep cycle to a starting as it relates to a hypothetical use to get me to the ramp up to 6 miles away?

 

[dingbat]

starting batteries have thicker plates, deep cycle batteries have more thinner plates.

Are you sure about that?

​

So, How Are Deep-Cycle Batteries Different?​

The thing that makes deep-cycle batteries "deep-cycle batteries" is that they are made with much thicker lead plates than traditional lead-acid-batteries.

These thicker plates allow deep-cycle batteries to be discharged and recharged over and over with minimal wear and tear.

 

[dingbat]

If I go non deep cycle what could I expect for performance of a deep cycle to a starting as it relates to a hypothetical use to get me to the ramp up to 6 miles away?

The grp. 27 deep cycle batteries I use for starting are rated at 109 amp hours each.

Gives me 750 MCA (600 CCA) of starting current. Mfg. calls for 570 CCA battery.
When battery switch is combined, I can spin the starter with 1,200 CCA

An automotive battery doesn’t carry an AH rating, but the reserve capacity (RC) rating will give you an idea.

RC is the number of minutes the battery will support a 25A load before dropping below 10.5V. Divide the batteries RC rating by the current draw of your trolling motor to covert to @ minutes of run time

 

[redneck joe]

Divide the batteries RC rating by the current draw of your trolling motor to covert to @ minutes of run time.

Well crap, math...

 

[redneck joe]

OK so 50 amp on a 115 rc is 2 plus hours and I'm assuming that is at full thrust so longer in running 50%

 

[redneck joe]

This is the one I'm eyeballing

https://www.oreillyauto.com/detail/c/extreme/super-start-extreme-standard-flooded-side-post-battery-group-size-78-800-cca-115-minute-rc/ssbp/78ext

 

[KD4UPL]

there are dual purpose batteries (starting and deep cycle). however generally starting batteries have thicker plates, deep cycle batteries have more thinner plates.

using a deep cycle as a cranking battery works until the cranking load overheats the plates and they warp, shorting out your battery.

what group number is your current battery?

look here for dimensions. https://batterycouncil.org/wp-content/uploads/2023/10/BCI-Group-Sizes.pdf

where would you want to move the batteries? I would probably install under the console

Exactly backward. Starting batteries need lots of amps fast. Amps come from surface area, thus more thinner plates in a starting battery. Deep cycle plates are thicker but fewer.
As long as a deep cycle has enough MCA (or CCA, whatever you're going by) it will work fine. And probably last longer due to heavier duty construction.