What batteries for bow thruster on 58LRC

[zigzag930]

The bow thruster batteries on our 58LRC appear to be giving out. They tested @ 13v (ea) and are wired in series for 24V. When I hit the thruster, the voltage drops from 26volts to 8-10 volts and the thruster runs very slowly.
Current batteries are Interstate 8DAGMD which are sealed AGM Deep cycle batteries. I would think that Deep cycle is not correct for a thruster considering they are high current draw for short time.
Any comments, suggestions? Considering 12v deka 8D's or maybe even 4D?

 

[divert00]

I use a pair if group 31 flooded lead acid batteries. Work well, not expensive, wide availability, but you must check water levels.

Also use same setup to start Cat 3406s.

John McCarley
Water Colors
Wrightsville Beach NC

 

[Captain Ralph]

Big sealed G31s is all you need.

How old are your batteries and how are they charged?

 

[zigzag930]

I've owned the boat for 4 yrs and haven't changed them, so at least 4 y/o, probably 5-6 y/o.
They charge via a separate 24v charger. Not sure if they also charge via the 24v alternator or not.

 

[Captain Ralph]

Yep, 4 years; toast.
This is what we have been installing for thruster batteries. Good service.
Deka makes them.

https://www.westmarine.com/west-marine-group-31-dual-purpose-marine-battery-100-amp-hours-700-cold-cranking-amps-860-marine-cranking-amps-190-reserve-minutes-19751684.html

 

[Boatsb]

The only grp 31 id use is the odyssea extreme. The west is pure junk I've pulled all sorts of their stuff out and got warranty on about 25% of it.

The thruster on that boat is big. The boat is big. The wind exposure is big. Its not a good place to put a grp 31 battery to begin with. Having the batteries die during a docking and hurting someone is not acceptable.

We almost always use 2 x 8D odyssea batteries for thrusters. Better safe than sorry.

 

[JD5652]

Zig -

I have a pair of Lifeline GPL-8DL wired to give 24 VDC. I have a separate 24 VDC battery charger to charge them. Mine are NOT charged by any alternator.

I replaced mine in 2019 and they are still going strong. These are Mil-Spec, Coast Guard Approved AGM batteries.

GPL-8DL AGM Battery - Lifeline Batteries

The GPL-8DL is a high performance, Mil-Spec, AGM battery, produced in the United States. Due to the Lifeline Battery's quality construction, it has an industry leading 2% per month self discharge rate at 77°F (25°C), compared to 10%+ for conventional batteries. Coast Guard approved, DOT Haz Mat...

lifelinebatteries.com

The batteries and charger are mounted underneath forward state room bunk compartment.