12V Bow Thruster Battery Replacement

We have a 12v 8D for our 12v Bow Thruster which needs replacement. I've seen some threads about swapping 8Ds for a couple of smaller sets. Anyone done this on their thruster? Appreciate any recommendations for a replacement.

I'm using a pair of Optima Red Top AGM batteries in parallel for my bow thruster. They're light and easy to handle, and have worked perfectly for a couple of years now with a 7.5 HP thruster.

How is your current battery charged?

I too have a pair of G31 AGMs in parallel. I didn't have much choice in brand - ended up with West Marine branded which I believe are Deka and fairly good batteries, but I could be wrong. Biggest hassle for you is you may need to re-arrange cables.

Peter

mvweebles said:

I too have a pair of G31 AGMs in parallel. I didn't have much choice in brand - ended up with West Marine branded which I believe are Deka and fairly good batteries, but I could be wrong. Biggest hassle for you is you may need to re-arrange cables.

Peter

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You can buy G31 AGMs on Amazon from Renogy, WindyNation or Weize for about $200 each.

David

Running down the charging. Unfortunately, our one-lines appear to be out of date, but I think we are connected to a trickle charge on shore power and then a 15a echo charger when off shore power.

A couple of SLA start batteries will work too, and are cheaper and perhaps more tolerant of older chargers. I have a personal preference for AGM, but either will work.

8d are ‘old school’ I swapped out 2 8d’s for 31 AGM. Everything spins faster

You can get Trojan 8D AGM batteries for $800. And 161 lbs weight.

JohnO said:

We have a 12v 8D for our 12v Bow Thruster which needs replacement. I've seen some threads about swapping 8Ds for a couple of smaller sets. Anyone done this on their thruster? Appreciate any recommendations for a replacement.

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Odyssey Extreme, ODX-AGM31 and you pick from post variant choices. (Previously, was PC-2150, but they've renamed their lines.) Very good cranking amps, decent capacity, no maintenance, not inexpensive.

A pair would be the bee's knees for a thruster... and in fact, last I read, that's what one of the thruster installation companies uses.

Lifeline AGMs wouldn't be a bad choice either, but for a thruster I'd choose Odyssey.

-Chris

Thrusters are essentially the same as a starting motor, so a start battery is best suited for that application. I had excellent success with Optima's, I used blue top 31's in series, with a dedicated 24V charger. Charging from the boat's 12V system is problemmatic, so I opted to connect the charger to the inverter to take care of charging while under way. 8D's are just a pain, really no advantage to using them for a thruster.

ranger58sb said:

Odyssey Extreme, ODX-AGM31 and you pick from post variant choices. (Previously, was PC-2150, but they've renamed their lines.) Very good cranking amps, decent capacity, no maintenance, not inexpensive.

A pair would be the bee's knees for a thruster... and in fact, last I read, that's what one of the thruster installation companies uses.

Lifeline AGMs wouldn't be a bad choice either, but for a thruster I'd choose Odyssey.

-Chris

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Thanks all - really appreciate the recommendations.

Ranger & Iggy, I'll check out the Odysseys ... I have a couple on my 4Runner and love them, but never tried them in the boat.

JohnO said:

We have a 12v 8D for our 12v Bow Thruster which needs replacement. I've seen some threads about swapping 8Ds for a couple of smaller sets. Anyone done this on their thruster? Appreciate any recommendations for a replacement.

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Use your house bank! 8Ds are dinosaurs and will soon break your back! Tie everything to your house bank and increase it's size if it isn't already 1000+amps plus in size; will probably need to increase the size of the cables, depending on distance. Then a separate bank of small size for a genset start bank. Makes life a lot simpler.

Yes... Two Group 31 are roughly equivalent to an 8D in storage capacity, and much easier to get on and off. I personally recommend THREE Group 31 to replace the 8D. Footprint is just a bit bigger.

Recommend: $399 each for AGM by Interstate - dual purpose - 3 year full replace warrantee.

Their flooded Group 31 only have an 18 month warrantee. Ours lasted 19 months, LOL. So, we went with AGM this second time around.

I have really come to trust Interstate, and have found them never to give a hassle when there is a failure. Recently did a warrantee swap on a Group 24 AGM up on the bridge for all the electronics. Full replace at 21 months, for a battery with a 24 month full replacement warrantee. No receipt needed. The replacement gets a brand new warrantee "clock" for 24 months. We cruise up and down the east coast, so the place I buy may not be the place I deal with for warrantee. Never had a problem.

There are cheaper alternatives to be sure. I'm simply telling you what I do.

i recently had a strange experience with Thruster batteries. I replaced 4 x 6v Golf Cart Liquid batteries (wired to provide 24v), with two GPL3100T 12 V Batteries from Lifeline last fall. I have purchased over a dozen large and small Lifelines since 2006 and they have always performed well....until now.

The New GPL3100T's wired in series to provide 24v could hardly power my Thruster and voltage dropped immediately. I rechecked all my power requirement calculations, thinking I had made a mistake withe the required amperage, and finally returned one of the batteries to Fisheries Supply last week. They called me today, the suspect battery was DOA and the provided a full refund of my purchase price.

ranger58sb said:

Odyssey Extreme, ODX-AGM31 and you pick from post variant choices. (Previously, was PC-2150, but they've renamed their lines.) Very good cranking amps, decent capacity, no maintenance, not inexpensive.

A pair would be the bee's knees for a thruster... and in fact, last I read, that's what one of the thruster installation companies uses.

Lifeline AGMs wouldn't be a bad choice either, but for a thruster I'd choose Odyssey.

-Chris

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I have a 24v system and use two 12v Odyssey Group 31 PC 1250 Batteries in series with a 12v 3 bank charger. The charger died for the second time in 4 years and I didn't know until I was getting low voltage warnings while I was docking. The Batteries had dropped to 11.5 volts but still drove the unit. I had trouble getting them to take a charge with a portable charger. The charger was telling me I had 2.8 volts in each. It took multiple tries but finally got them charged and they held. I ran the thruster at 75% until I got over heated motor warnings. They finished that at 12.5 volts. I got the new charger on them and I think they have survived. Crazy expensive but seem to be worth it. When one did not charge up I bought a new one. Like, $580. Cheapest I could find from Amazon delivered. Now I don't need it and Amazon won't take it back. Anyone have an interest in Southern California? I'll make a deal.

ranger58sb said:

Odyssey Extreme, ODX-AGM31 and you pick from post variant choices. (Previously, was PC-2150, but they've renamed their lines.) Very good cranking amps, decent capacity, no maintenance, not inexpensive.

A pair would be the bee's knees for a thruster... and in fact, last I read, that's what one of the thruster installation companies uses.

Lifeline AGMs wouldn't be a bad choice either, but for a thruster I'd choose Odyssey.

-Chris

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We went with two of the ODX-AGM31s for our new Vetus install partly because I didn’t want conventional FLAs under the forward berth. Also, Florida Bow Thrusters endorses them for their 1,150 cold cranking amps. Mine will be wired in series to provide 24V. Will be hooking them up later this week.

RickyD said:

I have a 24v system and use two 12v Odyssey Group 31 PC 1250 Batteries in series with a 12v 3 bank charger. The charger died for the second time in 4 years and I didn't know until I was getting low voltage warnings while I was docking. The Batteries had dropped to 11.5 volts but still drove the unit. I had trouble getting them to take a charge with a portable charger. The charger was telling me I had 2.8 volts in each. It took multiple tries but finally got them charged and they held. I ran the thruster at 75% until I got over heated motor warnings. They finished that at 12.5 volts. I got the new charger on them and I think they have survived. Crazy expensive but seem to be worth it. When one did not charge up I bought a new one. Like, $580. Cheapest I could find from Amazon delivered. Now I don't need it and Amazon won't take it back. Anyone have an interest in Southern California? I'll make a deal.

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Did you mean to write you have a 24v charger? With 2 12v batteries in series you effectively have one 24v power supply which should be charged with a 24v charger IMO.

~A

All you guys talking 24V, i posted a pair of 24V macerators for sale.

AlanT said:

Did you mean to write you have a 24v charger? With 2 12v batteries in series you effectively have one 24v power supply which should be charged with a 24v charger IMO.

~A

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My original set up from 2018 was a 3 bank 12v charger and two 12v batteries in series. This charger failed in 12 months. They replaced it under warranty with a new style which was supposed to be better. It was, it lasted 2 years. 3 year Warranty was based on original purchase date so they would not give me a refund. So, I bought a Sterling 24v charger. Just installed a week ago. So far I like it.

So I went with the recommendation of the ODX-AGM31 ... wired in parallel to juice up the CCAs. Quick question ... my main run to the thruster is with 3/0. No one around here carries 3/0 ... only 2/0 or 4/0. Thought 2/0 would probably be fine for a jumper. My resting voltage on shore power appears to be around 13.35 - 13.4 V. Curious what other ODX users see and what kind of drop and recovery I can expect on a ~3 sec burst.

Also, should I just beef up the jumper to 4/0? Thinking that might be better but would appreciate opinions. Thx.

JohnO said:

So I went with the recommendation of the ODX-AGM31 ... wired in parallel to juice up the CCAs. Quick question ... my main run to the thruster is with 3/0. No one around here carries 3/0 ... only 2/0 or 4/0. Thought 2/0 would probably be fine for a jumper. My resting voltage on shore power appears to be around 13.35 - 13.4 V. Curious what other ODX users see and what kind of drop and recovery I can expect on a ~3 sec burst.

Also, should I just beef up the jumper to 4/0? Thinking that might be better but would appreciate opinions. Thx.

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Larger cable is always better. I always go at least one size larger than required. It is a one time cost that will pay benefits forever in better voltage.

Thanks Dave - that's what I'm thinking. Bought the 2/0 and made the jumpers, but re-thinking that and will probably re-do it. $100 mistake would certainly not be the most expensive one I've made.

With the current draw of a thruster big cables are good insurance.

How long are these jumper cables? Are these between two batteries, meaning maybe 18 inches? At $100, guessing longer, but maybe you're fine.

Peter

JohnO said:

So I went with the recommendation of the ODX-AGM31 ... wired in parallel to juice up the CCAs. Quick question ... my main run to the thruster is with 3/0. No one around here carries 3/0 ... only 2/0 or 4/0. Thought 2/0 would probably be fine for a jumper. My resting voltage on shore power appears to be around 13.35 - 13.4 V. Curious what other ODX users see and what kind of drop and recovery I can expect on a ~3 sec burst.

Also, should I just beef up the jumper to 4/0? Thinking that might be better but would appreciate opinions. Thx.

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I used 4/0 with two ODX AGM31s and have VERY short runs—as in two feet or so. No idea what drop and recovery numbers are but I can’t imagine how I’d reduce cable losses any further. On my Vetus BOWB150 thruster, I could not fit 4/0 cable through the weatherproof glands and into the connection compartment. (VERY tight in there to be bending 4/0 even if I could have gotten it through.)

Vetus makes a connection kit for the BOWB models (it’s the BOWBHPCK, I believe) that puts the connection points on the outside of the thruster, vs trying to thread cable through the glands. Far from a walk in the park to hook up, but doable. I don’t like the cables being unsupported and suspended under the lugs, so will be installing blocks to support them. Also, still need terminal and fuse covers.

Used the thruster today for the first time moving the boat to Sarasota and it’s a joy.

I would cover the terminals in case you drop a wrench you don’t short out the batteries.

What do you need such battery power for? A single group 27 battery should do it for you.

pete

Pete Meisinger said:

What do you need such battery power for? A single group 27 battery should do it for you.

pete

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Not if the thruster is 24 volts.

Pete Meisinger said:

What do you need such battery power for? A single group 27 battery should do it for you.

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Depends on thruster and boat.

Ours, for example (Vetus BOW16024D, aka 250mm tunnel and 160 kg thrust 24VDC) specifies a minimum of 950 CCA and max of 1900 CCA. (Max may just mean beyond that, there's no additional benefit.)

For ours, Vetus suggests a minimum of two 125 Ah batteries (from among Vetus products, but maybe similar to G31s) or two 4Ds in series for the lower rating... and 4x in series/parallel for the higher rating.

Looks like Vetus recommends two 170 Ah batteries (from among their products) in series for a BOWB150. Don't see a CCA table to cross-reference from that... but maybe that'd be like two 4Ds. Or the Odyssey Extreme G31s, spec'd for serious CCAs.

-Chris