I hate 8D batteries. Replace with a pair of 27s or 31s?-gctid823048

[Cptmorgan]

My port 8D start battery is dead. The starboard start 8D is just fine.

I figure I can replace the 8D with a pair of group 27s or 31s for the same price as an 8D, and have a net gain in AH and MCA. Anyone using pairs of 27s or 31s as start batteries?

The Cummins BTAs need at least 1200 MCA in my experience. The preheaters are a battery killer.

[Norton_Rider]

I believe that there are a few people in this forum running a single group 31 battery per engine. There are readily available group 31s rated at 1100 and 1150 CCA.

[iceclimber]

https://www.walmart.com/ip/EverStart-Maxx-Marine-Battery-Group-Size-29DC/20531539

Been using these for years, yeah lower CCA, but also 100 bones, or even cheaper if you pass on the warranty. Paired up they do just fine, or even as a single.

[Uncle_Bob]

I changed my factory set-up of a dedicated starting battery for each engine to start both from one 8D. One alternator does the start battery and the other the house. Handles the pre-heaters fine. In other words one battery works well. It won't care if you get the cranking amps from an 8D or another configuration. Edmonds battery is a good source.

[aluxury1]

This one battery should last and do the job for quite a long time thus being the "best deal" for the dollar.

https://www.amazon.com/NorthStar-Ultra-Performance-Group-Battery/dp/B00P1K6EPE

[cosmo777]

On our 4788 (with 330 Cummins), I pulled out both 8Ds and installed Grp 31's - one for each engine.

Been this way for 2 years without a problem. Pre-heaters stil in place (not unplugged).

[Norton_Rider]

"cosmo777" post=823088 wrote:
On our 4788 (with 330 Cummins), I pulled out both 8Ds and installed Grp 31's - one for each engine.

Been this way for 2 years without a problem. Pre-heaters stil in place (not unplugged).

Do you boat year round? have you had any problems starting the engines in below freezing temperatures? I realize the water in our area stays between 45 and 50 degrees, but the lazarette will be somewhere in between the outside temperature and the water temperature.

[SomeSailor]

My truck with a Cummins 5.9L has two Group 31 batteries. Don't see why that wouldn't work well on a boat.They're Optima AGMs and are 900 CCA each.

[Cptmorgan]

Last winter, when the 8D started to show signs it was near the end of its,life I tried a single new Group 31 Deep Cycle flooded from another project to see how it would perform (1000 MCA / 833 CCA). The little 31 Deep Cycle was noticeably slower to crank in the cold weather than the near death 8D, so I ended up leaving it alone. Now that the 8D is truly dead, I need to fix the problem. I'd like 1200+ MCA to start the boat in the cold.

I'm running Blue Sea Battery Isolaroter/Combiners. I'll stick with a dedicated bank for each engine.

[Old_Man_With_A_Boat]

I have one 8D to start both engines. It has been this way since I bought the boat in 2002. Replaced it in 2012. It works great.

[bal734]

http://baylinerownersclub.org/index.php/forum/motoryachts/67307-replacing-8d-starting-battery

I have one group 31 per engine. Still going strong at six years.

[Norton_Rider]

"Cptmorgan" post=823102 wrote:
Last winter, when the 8D started to show signs it was near the end of its,life I tried a single new Group 31 Deep Cycle flooded from another project to see how it would perform (1000 MCA / 833 CCA). The little 31 Deep Cycle was noticeably slower to crank in the cold weather than the near death 8D, so I ended up leaving it alone. Now that the 8D is truly dead, I need to fix the problem. I'd like 1200+ MCA to start the boat in the cold.

I'm running Blue Sea Battery Isolaroter/Combiners. I'll stick with a dedicated bank for each engine.

To answer your original question, I don't think there's any doubt that two group 31s in parallel for each engine will work, since they will provide as much or more CCAs than an 8D.

In my mind the question is whether a single group 31 per engine will do it. In your experiment you used an 833 CCA battery. That's 28% less cranking power than a Northstar 1150 CCA group 31 battery. Here are the Cummins requirements for a 12 Volt starting system on a 6BTA marine engine. Note that JW stands for Jacket Water Cooled (like the 270 HP engine) and SW stands for Sea Water Cooled:

Minimum Recommended Battery Capacity

6B/6BT/6BTA-M (JW) Cold Soak at -18┬░C (0┬░F) or Above - Cold Cranking Amperes (CCA)... 950

6BTA-M (SW) Cold Soak at -18┬░C (0┬░F) or Above - Cold Cranking Amperes (CCA) ................ 1100

Reserve Capacity - minutes .................................................. .................................................. ....160

For comparison, here are the Northstar NSB-AGM 31 specs:

CCA rating at -18┬░C (0┬░F) 1150 A

CA/MCA rating at 0┬░C (32┬░F) 1370 A

Reserve capacity 220 min

[Johnny_Vintage]

I have 3 8D's in my 38. 1 to crank both Hinos and 2 for house. Was that way when we bought the boat. Worked well and I never changed to anything else. Buy the batteries from our Marina shop. They deliver them, pull the old ones out, then drop the new ones in. I give the two guys 20 bucks each for their help. They call it beer money. I call it awesome!!

I get 5 years out of the house 8D's.

JV

[Norton_Rider]

"Johnny Vintage" post=823115 wrote:
I have 3 8D's in my 38. 1 to crank both Hinos and 2 for house. Was that way when we bought the boat. Worked well and I never changed to anything else. Buy the batteries from our Marina shop. They deliver them, pull the old ones out, then drop the new ones in. I give the two guys 20 bucks each for their help. They call it beer money. I call it awesome!!

LOL... I do the same thing. My mechanic gets Interstate 8D batteries at a super low price. He and his son deliver and install them. I send them Amazon.com gift certificates every Christmas. The reason that I want to get rid of the 8Ds is to lighten the boat a bit and take care of a slight list.

[redskyjoe]

I have twin 315 HP Cummins in my boat. When I bought it last yr it had a single 8D battery to start both engines. When that battery died I replaced it with a single 4D battery just because I didn't want to wrestle an 8D back in there and have had no issues starting the engines. Admittedly, I haven't tried starting the engines in freezing temps so can't comment on the 4D's ability under those conditions.