Deep cycle battery questions

tailhook · Post by **tailhook** » Thu May 16, 2019 12:15 pm

Hi everyone,

I'm a newer boat owner and even newer to deep cycle batteries.

When I first purchased the boat, I installed brand new batteries in it, that was close to 3 years ago. This past week I was on the water and noticed the trolling motor was performing a bit under par, despite the charging bank showing full the night before. On the highest speed, it will usually throw me overboard and it's nowhere near that. I checked the TM prop and shaft and it looked good.

So, when I put the boat away I charged back to full and checked the voltage the following day. Battery 1 read 10.5 V and battery 2 read 8.8 V - this is measuring between terminals. From what I've gathered, in a resting state (24 hours after fully charged), a deep cycle battery should read at least 12.6 V or it is considered discharged. Then I started reading about 24 V systems and I got completely lost...

I also checked the water level in each cell and it looks good (about 1/8" below the vent tubes), so I don't think that's the cause.

Any advice? Am I on the right track? Is it time for new batteries? Any help is appreciated

ash · Post by **ash** » Thu May 16, 2019 12:29 pm

Hey Tail Hook,

Depending on use, size and charging habit 3-4 years is about right. Without Load testing the battery you should get 12.5+v pole to pole on each battery. if you have one reading 8v it most likely has a dead cell or two but you have two batteries reading low voltage your probably running o reduced amps as well which is why shes running slow.

The crappy part with 24-36 volt systems when we wire them in series one bad battery in the series will draw down the rest of the batteries and over time they all go south or lose amps. So you are not replacing one at a time you're doing 2 at a time.

Go with the largest reserve capacity that will fit your boat ie size 27 or 30 as you will get more amphours. If your budget can handle it look at AGM or gel batteries as they wont take the beating that a lead plate battery will - I picked up Duracell AGM size 30 at Sams Club for 150 each but I imagine they will hold in the full 4-5yrs vs the everstarts i was running.

Also check how your wired and wire it back the same

: 24-volt-battery-1.jpeg (17.32 KiB) Viewed 1310 times

Dave A · Post by **Dave A** » Thu May 16, 2019 2:30 pm

Yep, what Ash said. I get 3 - 4 years out of mine typically with proper maintenance. Probably closer to 3.

Hughsonbassin · Post by **Hughsonbassin** » Thu May 16, 2019 6:17 pm

I’m on 6 years with 3 srm-31 interstates. Batteries are hit or miss sometimes just like any manufactured part

ash · Post by **ash** » Fri May 17, 2019 10:12 am

Hughsonbassin wrote:I’m on 6 years with 3 srm-31 interstates. Batteries are hit or miss sometimes just like any manufactured part

Also depends on how you charge em and the water you run if your running rough water like the delta and gettin air those batteries are taking a beating and will drop plates - thats why the AGM is worth it in bass boats IMHO -

WRB · Post by **WRB** » Fri May 17, 2019 7:33 pm

You also want to check the onboard charging system and terminal corrosion. Wet cell batteries can easily be over charged with a defective charger cooking the battery plates and oxides fill the bottom case shorting out a cell. 8V indicates 2 shorted cells. If you can see dry plates they are toast.
A new 3 bank onboard charger with 15 amps per bank, auto shut and maintence modes may be in your future. Marine deep AGM's cost more and last 2x to 3X longer the wet cells. If you have room go with group size 31 for the TM, 27 Marine cranking battery for normal use, 29 if you have newer state of the electronics/sonar units. The good thing about AGM is maintenance free and low corrosion issues.
Figure batteries as a normal maintenance cost with boats, like tires they wear out in time. Not to change the subject but trailer tires should be changed every 5 years regardless of wear.
Welcome to boating!
Tom