Batteries......what would you do

[steved]

My recently purchased boat is fitted with a 6 x 2V domestic battery set up, they are Rolls S2 1275Ah AGMs, so loads of Ah.

When I surveyed the boat I noted that the casing on one the battery's was cracked and split, with the top of the battery a bit swollen, the voltage on this battery was reading about 2.2, compared with 2.35 on the remaining 5. The batteries are original fit, so 9 years old. These batteries also start the generator.

The engine has 2 alternators, one for domestics, and one for engine start battery.

Cost to replace all the batteries on a like for like basis is around £2500. So, could I get away with just replacing the bad battery, or just bite the bullet and replace them all.

OR

Consider changing the domestics setup (lithium?), but not sure what the cost would be to achieve the same Ah, plus the need for a separate generator start battery.

The boat will be used extensively, with a split of 50/50 between shore power and off grid.

What would you do?

 

[Greg2]

Lifespan estimates for the S2 appear to be 12 years on average so replacing the one that is damaged wouldn’t be my first choice as you would have one new battery with the rest getting on towards their likely end of life. That said, it might be a compromise option if you want to put off shelling out having just bought the boat and it might well be absolutely fine for several years.

Lots of lithium advocates on the PBO forum but they are not for me so I would be thinking about replacing the whole bank. Rolls are obviously a good option but you could look at less expensive options.

As an aside, are you keeping the Nordic?
.

 

[PaulRainbow]

My recently purchased boat is fitted with a 6 x 2V domestic battery set up, they are Rolls S2 1275Ah AGMs, so loads of Ah.

When I surveyed the boat I noted that the casing on one the battery's was cracked and split, with the top of the battery a bit swollen, the voltage on this battery was reading about 2.2, compared with 2.35 on the remaining 5. The batteries are original fit, so 9 years old. These batteries also start the generator.

The engine has 2 alternators, one for domestics, and one for engine start battery.

Cost to replace all the batteries on a like for like basis is around £2500. So, could I get away with just replacing the bad battery, or just bite the bullet and replace them all.

OR

Consider changing the domestics setup (lithium?), but not sure what the cost would be to achieve the same Ah, plus the need for a separate generator start battery.

The boat will be used extensively, with a split of 50/50 between shore power and off grid.

What would you do?

Lithium, no question.

The Rolls are only good for 50% DoD, so usable 600Ah ish. A 314Ah LFP will give you 250Ah usable.. 3 of those with grade A, quality cells and each having it's own BMS gives you 750Ah (if you really need that much) and would be significantly less money than replacing the Rolls. No need for a separate generator battery, the LFP will start it just fine.

 

[Refueler]

My initial thought - I'm always amazed at the variations of battery types / installations found on boats ...

With regard to OP's 6 x 2V cells .... they must fill quite a space ? And makes me wonder why installer used such a config. As OP has found - its not a cheap setup. As per 'Greg2' ... I would not just replace one cell as you have no idea how long before the others start to fail.

I would be inclined to sit and work out the amount of power needed on the boat and then consider replacing the whole lot with 2 12V AGM's in parallel ... surely has to be cheaper and more easily serviced ?
Or go Pauls Li route ... BUT take care to make sure the Li battery(s) chosen can actually start an engine ... as like Lead Acid - there are those that can and those that should not !!