AGM Batteries.. replace as before… or?

As with most things boat (or indeed any consumer choice!) choose what suits your needs best. Expensive AGMs suit a particular pattern of usage, but it may be a waste of money buying something that you cannot fully utilise.
 
You can get some good quality 120AH AGMs for £150. If you're looking to save a bit of money and don't feel you need top of the range AGMs, then this could be a good solution for you. If it's any endorsement, I've been using these types of AGMs for the last 7 years or so and have been pleased with them.
 
If you pull large loads such as with a winch best to check the specs for the internal resistance of the battery, I had issues with low voltage alarms on my radio and instruments dropping out when running a powered winch.

Two issues were the manufacturer had not run a separate 25mm feed to the winch but relied on one to feed all the domestic side. I fixed that but discovered the battery was also causing a bad voltage drop, replaced it with a Rolls AGM and all was good. Ideally I should have a dedicated battery for the winch but I don't have the space.
 
jwfrary said:
If you get half of the 13 years with the new set I think you will be well served!
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Life of batteries is a function of the number of charge/discharge cycles and the average depth of discharge. Big advantages of AGMs is that they will withstand greater discharge over a longer number of cycles, accept charge at a greater rate and have a slow self discharge rate. This is why the OPs batteries have lasted that long even though he says they have been maltreated.

They are popular with heavy users such as liveaboards (as are some FLAs with high cycle ) but may be a waste for the "weekend" type user, hence my observation in post#2. Rolls are at the upper end of the price bracket, and there is a strong correlation between price and life for a given capacity. A nominal 95Ah Rolls is £215 - a deep cycle FLA at the other end is less than £100 - The Exide AGM (usually used in vehicles such as Range Rovers) is around £130. Mine are 6 years old (5 of them, one engine start, one bow thruster, 3 service) and I shall be most disappointed if they don't last at least 10 years. My demands are moderate, the service bank is of a size such that it never gets heavily discharged and I periodically top up to fully charged with shorepower.

The 128s the OP currently has are £270 each and guess he has at least 2, but probably more in his service bank. Replacement is a big investment and probably wise to consider the expected pattern of usage and charging arrangements before deciding. There are plenty of good AGMs of that capacity at around £100 less each that may well be suitable.
 
It all depends on how you plan to use them. If they're only going to experience limited discharges, AGMs are fine. If you routinely intend to deep-cycle them, then the Trojan T105s which PaulRainbow suggested will no doubt last longer.
 
pvb said:
It all depends on how you plan to use them. If they're only going to experience limited discharges, AGMs are fine. If you routinely intend to deep-cycle them, then the Trojan T105s which PaulRainbow suggested will no doubt last longer.
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Paul knows me and knows the boat. He doesn’t have the highest opinion of the previous owners’ approach to electrical matters, and he knows that I am completely incompetent electrically!

The regular cause of battery abuse has been a very “demanding” gas detector, hard wired…??…

The boat has eight Rolls 128s. Two are engine start and six are house bank. The batteries live under the saloon settees, so going over to Trojan T105s, which I agree with Paul about, would entail a deal of carpentry.
 
Kukri said:
The boat’s Rolls S12-128 AGMs have died, which is not surprising as they are 13 years old and had been brutally and repeatedly maltreated.

Before I replace like for like, is there any reason why I should not do so?
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Don't AGMs need a special charging system? If so, buy similar batteries so you don't have to change the charging system. I am no expert on batteries of chargers. it is just a bit of gossip I overheard.
 
Trojan 105's are not cheap, you need space for them and they need regular maintenance or they will fail prematurely.

AGM batteries are low maintenance and if specified and charged properly will last a long time. They are better suited for some users.

I would wreck the 105's without even trying.

It's the not trying that will ruin them, for me life is too short. You mileage may vary.
 
Lucy52 said:
Trojan 105's are not cheap, you need space for them and they need regular maintenance or they will fail prematurely.

AGM batteries are low maintenance and if specified and charged properly will last a long time. They are better suited for some users.

I would wreck the 105's without even trying.

It's the not trying that will ruin them, for me life is too short. You mileage may vary.
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T105s cost about £140 each, Rolls are about £260 each.

"Regular maintenance" consists of periodically checking the electrolyte and topping up as necessary. Less checking and maintenance than an engine.
 
Rolls batteries offer a long life but are one of the most expensive brands available.

I would still abuse the T105's In "oops I forgot" moments.

My sealed maintenance free batteries ran down twice during lock down when the electricity ran out. They are holding up well. are no trouble and won't cost a lot to replace.
 
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