AGM Batteries

[Greg2]

We are thinking of replacing our domestic and engine start batteries with AGM batteries. Anyone have any experience of these - are they worth the extra cost and do they do better than standard lead acid batteries?

 

[DavidJ]

We have all gone through battery loops and I think for many have arrived back where we started with lead acid.
Sealine had a preference for all lead acid deep cycle (leisure) 2+3 and I got 6/7 years out of mine twice. The yard changes my batteries last year and put in all lead acid starting batteries which I think is the preference of Princess
I conclude on that one that it really doesn’t matter for normal boat use.

 

[Tranona]

Depends on your pattern of usage. In general if batteries are looked after - that is not discharged regularly below 50% capacity and kept at full charge through longer periods of inactivity AGMs typically will have more than 50% longer life than FLAs for about 33% extra cost. So on this basis the answer is yes.

In this broad usage regime typical life in UK summer use, winter layup you can expect 6 years from FLA and 10+ years from AGMs. In addition AGMs have higher charge acceptance rates and lower self discharge rates. The adoption of AGMs for automotive use has resulted in a significant fall in the price of AGMs so if you have a long time horizon it is a no brainer.

Different kind of boat, but principles the same, I have just bought the batteries for my project sailing boat with 30hp engine. 2* Exide 95Ah AGMs usually used in Jaguars £230 compared with 2*105Ah Numax £195 I had the same Exides in my last boat and they were still going strong at over 6 years when I sold it. Engine start is an Odyssey 34Ah lightweight high power AGM which is roughly half the volume of a similar FLA start battery, but expensive at £165. However I have a similar type Red Flash in my Morgan which is now approaching 19 years old! If I had the space, though I would probably fit an automotive AGM of about 65Ah at about half the price.

 

[Greg2]

Two differing perspectives, which is interesting.

@Tranona if AGM is the way to go is it worth getting better quality such as Rolls do you think?

 

[Tranona]

Again depends on your pattern of usage. If you are a liveaboard for example then your demands on your batteries and systems are higher so worth considering spending more. However for weekend and holiday type use probably not. The big jump in potential life comes from the change in type then incremental changes as you get up the price scale, usually in terms of more robust plates and increase in size and weight for a given capacity. You can look at the data sheets and see the total discharge cycles to help differentiate one battery from another as this gives you an idea how much potential extra life you get for the money. Inevitably you also have to consider how long you are planning to keep the boat as in the early years there is little difference in performance.

 

[ashtead]

If you fit AGM do you have to change any components charging them ? I guess an inverter works for all types but just curious. What about having AGM for the starter battery but not others if costs an issue?

 

[RobbieW]

If you fit AGM do you have to change any components charging them ? I guess an inverter works for all types but just curious. What about having AGM for the starter battery but not others if costs an issue?

You dont *have* to change any other components but it should be realised that AGM batteries have a slightly different set of charging parameters than wet or sealed lead/acid. They wont be damaged by using the same settings but you wont be using them to get advantage of their capabilities. In retrospect, I went a bit OTT after removing an unreliable genset and relying on engine charging (liveaboard in the Med at the time) by installing a 160A alternator with a Balmar controller. I like having the ability to control the charging cycle that the Balmar controller gives but the full alternator capacity was never used (about 110A was the higest I saw during the bulk phase and then only for 5 mins or so) - didnt have solar at the time. 12 years on from putting in the AGMs they are still there but the boat is getting little use at the moment, thats a 720Ah AGM house bank and a Red Flash AGM engine start.

 

[IDAMAY]

Yes, you may need to adjust your battery charger so that it knows what type of battery it is servicing. May make things more complicated if you have a mixture of battery types.

 

[Daydream believer]

I had a pair of 100 amp agm domestic batteries & I sure that I never ran them below 50%. However, after the 2 year warranty ran out they did not seem to be giving me the stated capacity. I discarded one & the other is used in my workshop to power a chinese diesel heater. But i need to have the battery charger connected to it after an hour. It is now 5 years old.
The Red Flash 35 amp starter battery I had also failed hopelessly. Totally flat & not accepting any charge whatsoever. I only realised that after one season & 2 laid up winters so I missed out on the warranty.
I have 2 more 100 amp AGMs at £ 180-00 each & another red flash £ 165-00 ( have to have that as it is all I can get in the void). They have been in since 2019 so have had little use. ( covid, lockdown etc). I now disconnect them over winter & this means that they stay fully charged when in storage. I just hope that they still produce the expected capacity, although at the end of last year I did notice the voltage dropping fast. I do not have fridge etc, just nav instruments, AV 100 autopilot ( when it works!!) plus nav lights.
The shore charger is a triple stage Dolphin 15 amp & the output has been confirmed as within acceptable limits by the battery manufacturer
If I have hassle I will go back to cheap lead accid as my original Varta ones lasted 7 years. The difficulty is finding a battery that fits the silly tight space that Hanse have provided.

 

[Tranona]

If you fit AGM do you have to change any components charging them ? I guess an inverter works for all types but just curious. What about having AGM for the starter battery but not others if costs an issue?

Depends. normally no except you might have to change the charging profile on the mains charger, but most modern chargers have this facility. The normal alternator should be OK unless you massively increase the capacity.

An AGM is less important for a start battery as it gets so little use. However a normal automotive 65Ah or so only has a premium of around £30 over an FLA. The reason for having an expensive Red flash (which is now £230!) is for space reasons. However the Odyssey equivalent I just bought was "only" £165, but I had built my box around this size to avoid creating another battery space elsewhere with the attendant work and cabling costs. I got 190Ah house and the start in a box just under 500mm square.

The real benefit of AGMs is in house applications with the faster charge acceptance and greater total cycles.

 

[JOHNPEET]

Again depends on your pattern of usage. If you are a liveaboard for example then your demands on your batteries and systems are higher so worth considering spending more. However for weekend and holiday type use probably not. The big jump in potential life comes from the change in type then incremental changes as you get up the price scale, usually in terms of more robust plates and increase in size and weight for a given capacity. You can look at the data sheets and see the total discharge cycles to help differentiate one battery from another as this gives you an idea how much potential extra life you get for the money. Inevitably you also have to consider how long you are planning to keep the boat as in the early years there is little difference in performance.

So with regard to some of the cheaper products on the market such as “Energy Expedition Plus” or ”Leoch” , some of which are offering 4 and 5 year warranties, what is the general opinions of these - reasonably good buys, or stay well away?

 

[Tranona]

Quite different products. The first offers either FLA or AGM at the low to middle price point. sold through ebay, but seem to offer nothing you cannot get with a basic branded battery such as Varta or Numax. Leoch are up market higher cost AGMs similar to lifeline.

When choosing batteries it is sensible to look at your usage pattern and determine what type is best for you. For most weekend and holiday type boaters cruising in the UK with a mixture of on the hook and shorepower, a decent size bank reflecting daily usage and efficient engine charging capacity a good leisure type FLA is fine, but if you are wanting longer life then it is worth going up to basic AGMs as the %age extra cost is exceeded by the potential extra life. If, however you live aboard, spend long periods off shorepower or boat in hot climates your needs will differ and you have to consider other power strategies.

 

[JOHNPEET]

Quite different products. The first offers either FLA or AGM at the low to middle price point. sold through ebay, but seem to offer nothing you cannot get with a basic branded battery such as Varta or Numax. Leoch are up market higher cost AGMs similar to lifeline.

When choosing batteries it is sensible to look at your usage pattern and determine what type is best for you. For most weekend and holiday type boaters cruising in the UK with a mixture of on the hook and shorepower, a decent size bank reflecting daily usage and efficient engine charging capacity a good leisure type FLA is fine, but if you are wanting longer life then it is worth going up to basic AGMs as the %age extra cost is exceeded by the potential extra life. If, however you live aboard, spend long periods off shorepower or boat in hot climates your needs will differ and you have to consider other power strategies.

My plans are for high usage weekends and extended weekends. Retired so lots of time available. My choice to go for AGM was also led by the house bank being able to be located beneath the aft cabin berth. Then keep all the banks of the same type for charging purposes.
Both of the above I found on the Alpha- batteries website.
Just interested to know what is good and what is not!

 

[Greg2]

Depends. normally no except you might have to change the charging profile on the mains charger, but most modern chargers have this facility. The normal alternator should be OK unless you massively increase the capacity.

An AGM is less important for a start battery as it gets so little use. However a normal automotive 65Ah or so only has a premium of around £30 over an FLA. The reason for having an expensive Red flash (which is now £230!) is for space reasons. However the Odyssey equivalent I just bought was "only" £165, but I had built my box around this size to avoid creating another battery space elsewhere with the attendant work and cabling costs. I got 190Ah house and the start in a box just under 500mm square.

The real benefit of AGMs is in house applications with the faster charge acceptance and greater total cycles.

Our usage is currently weekends and holidays but we may spend a lot more time aboard in the foreseeable future so I guess we are planning ahead. Cost is obviously a factor but as part of the work we are doing to get the boat how we want it isn’t significant and we woul’t want to ‘spoil the ship for a hap’orth of tar.’

 

[Hurricane]

I get through batteries.
Maybe because I leave them on charge all the time and mistreat them when I actuall use them.
I only get about 4 years use from a set of house batteries.
The last set were AGMs and didn't last any longer.
AGMs are a little safer but I have now gone back to standard flooded cell batteries.
This time, buying a known brand - Varta - I found a good Spanish supplier who delivers to the marina and the marina staff put them on the back of the boat for me.
The standard Varta J2 just about fits in my battery boxes so I am now considering batteries as a consumable and not worrying too much if I have to replace them.

 

[Daydream believer]

Further to my post#9 I have just reconnected the batteries & all 3 show 12.9-13 V . I put the shore power charger on for 24 hours & it showed that it was only adding a trickle charge so disconnected it on the basis that they were still well charged. 2 days later I filled my water tank & as I wanted to run fresh water through the pipes to flush them I ran the water for just under 4 minutes & the current discharge showing on my meter showed 5 amps. ( I was not connected to shore power). The voltage dropped to 12.4V almost immediately.
I stopped & it rose to 12.5 after 30 mins then a day later the voltage had risen to 12.7. this according to most tables is less than 90% . The NASA BM1 suggests about 75%.- but that may be a calibration issue after 5 months- I am somewhat surprised to loose 10% of capacity after 4 minutes at 5 amps on 2 No 100 amp batteries.
Is that something that one might expect?

 

[Hurricane]

Further to my post#9 I have just reconnected the batteries & all 3 show 12.9-13 V . I put the shore power charger on for 24 hours & it showed that it was only adding a trickle charge so disconnected it on the basis that they were still well charged. 2 days later I filled my water tank & as I wanted to run fresh water through the pipes to flush them I ran the water for just under 4 minutes & the current discharge showing on my meter showed 5 amps. ( I was not connected to shore power). The voltage dropped to 12.4V almost immediately.
I stopped & it rose to 12.5 after 30 mins then a day later the voltage had risen to 12.7. this according to most tables is less than 90% . The NASA BM1 suggests about 75%.- but that may be a calibration issue after 5 months- I am somewhat surprised to loose 10% of capacity after 4 minutes at 5 amps on 2 No 100 amp batteries.
Is that something that one might expect?

Voltage on its own won't tell you the battery's state.
To fully check a battery, you need to put it under load and see how the voltage then responds.
There are modern, more technical, testers but I use the crude old method - a tester like this:-

Battery Drop Tester 6/12V | BT91/7 | 1 Year Guarantee | Sealey

Generally, I connect it up, switch the load on for about 5 seconds - if the battery voltage drops to 9v or less - that battery is dead and needs replacing.
You have to be careful with load testers - you don't want to damage a good battery so don't use too often and don't load for too long.

 

[mil1194]

Voltage on its own won't tell you the battery's state.
To fully check a battery, you need to put it under load and see how the voltage then responds.
There are modern, more technical, testers but I use the crude old method - a tester like this:-

Battery Drop Tester 6/12V | BT91/7 | 1 Year Guarantee | Sealey

Generally, I connect it up, switch the load on for about 5 seconds - if the battery voltage drops to 9v or less - that battery is dead and needs replacing.
You have to be careful with load testers - you don't want to damage a good battery so don't use too often and don't load for too long.

I’ve got one almost identical to this bar the colour. It’s simple and it works.

 

[BartW]

In our business (Outside Broadcast Vans) we are used to use Gel Battery's, and were alway's very pleased with that, (curenly we use Li ion)
I never experienced nor heard of a real benefit going for AGM,

but imo more importantly,
use a high quality charger with multi stage charging algorithm; for me I would only use Victron or Mastervolt
install a battery monitor, and never discharge below 50% (i've set the alarm at 60%)
use a known brand for the battery's sa Varta, Victron, Bosch, ...
don't pay a premium for the supposedly "high end " brands

make sure that the batterybank is corrrectly wired ! very imprtant !
make sure that the battery's from one bank are replaced all together with new from the same badge !

all imho

 

[Portofino]

Is there a zero maintenance angle to factor in the choice?

It’s just the ER s get hot esp in the Med and maybe FLA need regular topping off with distilled water that’s extra evaporating in the heat = shorter than expected life .

AGM s are sealed maintenance free I understand so that’s one less thing ( to water level check ) to go wrong .
And things do go wrong on boats as we all know !