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Old 02-20-2023, 01:14 PM   #1
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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.
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Old 02-20-2023, 01:20 PM   #2
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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?
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Old 02-20-2023, 02:05 PM   #3
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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.

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Old 02-20-2023, 02:53 PM   #4
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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
You can buy G31 AGMs on Amazon from Renogy, WindyNation or Weize for about $200 each.

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Old 02-20-2023, 03:04 PM   #5
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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 Unfortunately, our one-lines appear to be out of date, but I think we are connected to a trickle charge on shore power and then a 15a echo charger when off shore power.
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Old 02-20-2023, 04:27 PM   #6
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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.
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Old 02-20-2023, 04:52 PM   #7
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8d are ‘old school’ I swapped out 2 8d’s for 31 AGM. Everything spins faster
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Old 02-20-2023, 06:51 PM   #8
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You can get Trojan 8D AGM batteries for $800. And 161 lbs weight.
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Old 02-21-2023, 06:58 AM   #9
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Quote:
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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.
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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Old 02-21-2023, 08:04 AM   #10
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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.
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Old 02-21-2023, 09:16 AM   #11
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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
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Old 02-21-2023, 09:51 AM   #12
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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.
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Old 02-27-2023, 02:00 PM   #13
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Quote:
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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.
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.
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Old 02-27-2023, 03:36 PM   #14
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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.
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Old 02-27-2023, 08:02 PM   #15
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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.
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Old 02-27-2023, 08:55 PM   #16
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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
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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Old 02-27-2023, 09:31 PM   #17
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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
We went with two of the ODX-AGM31s for our new Vetus install partly because I didnít 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.
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Old 02-28-2023, 08:52 AM   #18
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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.
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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Old 02-28-2023, 10:15 AM   #19
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All you guys talking 24V, i posted a pair of 24V macerators for sale.
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Old 02-28-2023, 11:27 AM   #20
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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
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.
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