AGM replacing lead acid batteries

[NBDensie]

I am planning to replace my knackered 3 year old domestic batteries with AGMs.  I guess they are knackered from being left undercharged for 6 months during last winter and lock-down as we are careful not to allow them to allow them to drop to a low voltage in normal use .  Mostly they are charged from a 120 Amp alternator but occasionally from a Victron invertor/charger. I am hoping that AGMs will suffer less whilst not in use.

 

Do I need to change the alternator or the Victron in any way?  I am getting different stories.  The Victron manual states that the charger default settings are OK for their own AGM batteries but doesnt comment on other brands.  However some web pages give dire warnings.

 

Many thanks

[WotEver]

24 minutes ago, NBDensie said:

The Victron manual states that the charger default settings are OK for their own AGM batteries but doesnt comment on other brands.

It can't, without knowing the spec.  Unfortunately, neither can we.  What are the manufacturer's figures?

[NBDensie]

I have not bought the AGMs yet and was hoping to resolve issues before being surprised by them.  The boatyard suggested that it did not matter much, but some web pages disagree.  Perhaps there are particular brands where it's a problem.

[WotEver]

14 minutes ago, NBDensie said:

Perhaps there are particular brands where it's a problem.

Absolutely.  The manufacturer will supply charging figures for their batteries.

[Tony Brooks]

45 minutes ago, NBDensie said:

I am planning to replace my knackered 3 year old domestic batteries with AGMs.  I guess they are knackered from being left undercharged for 6 months during last winter and lock-down as we are careful not to allow them to allow them to drop to a low voltage in normal use .  Mostly they are charged from a 120 Amp alternator but occasionally from a Victron invertor/charger. I am hoping that AGMs will suffer less whilst not in use.

 

Do I need to change the alternator or the Victron in any way?  I am getting different stories.  The Victron manual states that the charger default settings are OK for their own AGM batteries but doesnt comment on other brands.  However some web pages give dire warnings.

 

Many thanks

 

Be very wary. One supplier of AGM's has stated on their website that their AGMs need a higher than typical charging voltage. This means that to meet their requirements you would in most cases need an Sterling A to B. That another £300.

 

Certaily earlier designs of AGM needed a lower charging voltage than is typical on modern alternators. All this means that unless we van find the manufacturer's data you question can't be answered.

 

I would also comment that with any sealed batteries including AGMs you will find it far more difficult and time consuming doing DIY diagnosis in the early stages of a fault occurs or they sulphate. You will wreck AGMs almost as fast as wet open cells if you do no look after them properly. I believe they do have a sightly lower self discharge rate than wet open cells but they are likely to sulphate just as fas when left at less than fully charged.

[Tony Brooks]

22 minutes ago, NBDensie said:

I have not bought the AGMs yet and was hoping to resolve issues before being surprised by them.  The boatyard suggested that it did not matter much, but some web pages disagree.  Perhaps there are particular brands where it's a problem.

Absolutely - one supplier with a depot not that many miles away from Braunston got very shirty and threatened legal action when pressing them to justify what they were saying. I got the impression that they had no idea about battery charging and were just trying to avoid potential warrantee claims.

 

As long as the charger or alternator's absorption/regulated volatge is less than the manufacturer's maximum charging voltage there shoudl be no problem with fully charging them. The time it takes to get them fully charged will be affected by the charging voltage, the lower the voltage the longer the time needed.

[cuthound]

Be aware that not all AGMs are the same.

 

My Lifeline AGMs are 13 years old and still have over 50% of their original capacity. However they are not cheap to buy. They will also tolerate higher charging voltages and even a 16 volt equalising charge.

 

The reason why they have lasted so long is because they are either being charged by daily cruising or by a charger on a landline.

 

No lead acid battery will tolerate being left off charge for months on end. It is just as easy to destroy expensive batteries as cheap ones. ?

 

If you intend to do this, then it is better to buy wet lead acid batteries and a solar panel to keep them charged.

Edited October 3, 2020 by cuthound
To remove a spurious letter.

[NBDensie]

Thanks Tony, that is very reassuring  and with the caveat of over-high voltages there should not be a problem.  From Cuthound's reply I dont see that as likely. I am hoping that higher quality AGMs will suit our useage pattern rather better than Midland Chandler's special offer wet batteries, and will require less frequent replacement, especially now that we are losing the strength and confidence to manhandle 25 kg boxes into a rather confined space.  It seems worth trying them.

 

When out we run the engine every day and in the marina would hope to recharge perhaps once a month.  However this year lock-down meant we were not allowed on site until July.  

[Higgs]

1 hour ago, Tony Brooks said:

Absolutely - one supplier with a depot not that many miles away from Braunston got very shirty and threatened legal action when pressing them to justify what they were saying. I got the impression that they had no idea about battery charging and were just trying to avoid potential warrantee claims.

 

As long as the charger or alternator's absorption/regulated volatge is less than the manufacturer's maximum charging voltage there shoudl be no problem with fully charging them. The time it takes to get them fully charged will be affected by the charging voltage, the lower the voltage the longer the time needed.

 

I think it would be a difficult decision to leave a battery charger on, not knowing when you'll be allowed to check on things. Would it not be possible to charge the batteries up and disconnect them? ?? Leaving them charged. 

 

 

[Tony Brooks]

4 minutes ago, Higgs said:

 

I think it would be a difficult decision to leave a battery charger on, not knowing when you'll be allowed to check on things. Would it not be possible to charge the batteries up and disconnect them? ?? Leaving them charged. 

 

 

They would still self discharge but 40Watts + of solar would sort that even in winter.

[Tony Brooks]

19 minutes ago, NBDensie said:

Thanks Tony, that is very reassuring  and with the caveat of over-high voltages there should not be a problem.  From Cuthound's reply I dont see that as likely. I am hoping that higher quality AGMs will suit our useage pattern rather better than Midland Chandler's special offer wet batteries, and will require less frequent replacement, especially now that we are losing the strength and confidence to manhandle 25 kg boxes into a rather confined space.  It seems worth trying them.

 

When out we run the engine every day and in the marina would hope to recharge perhaps once a month.  However this year lock-down meant we were not allowed on site until July.  

 

Its a question of how long you run the engine for every day. If you only run a few hours per day and only fully recharge once a month then you will sulphate the AGMs in a similar time to wet lead acids.

 

I can see nothing in your original post to suggest that AGMs would perform any better than wet lead acids apart the the alleged lower self discharge  over lock down.By and large battery life is all about trying to keep to the 50% then recharge thing and very regularly fully charging the bank. Fully charging once a week is about the maximum period to minimise, but not prevent, sulphation.

 

Also I very much doubt the Victron charger fully recharges the bank if its only on overnight or for the odd day at a time. They tend to drop to float well before the batteries are fully charged. As an experiment when it drops to float turn the charger off and then on again. If the batteries are fully charged it will drop to float within  a very few minutes, if not it will stay in absorption for a while.

 

The life of a bank tolerably well matched to your demand is far more related to how well monitor their state of charge, how often you charge your batteries and how long you leave them even partially discharged than the  design of the battery.

[ditchcrawler]

3 hours ago, Tony Brooks said:

They would still self discharge but 40Watts + of solar would sort that even in winter.

That is what I have, I often take the small panels off when we cruise because it makes it easier walking on the roof, but they go back on once we get back to the moorings, saves worrying about a shore supply, has it tripped, galvanic isolation etc.

[GUMPY]

2 hours ago, Tony Brooks said:

Also I very much doubt the Victron charger fully recharges the bank if its only on overnight or for the odd day at a time. They tend to drop to float well before the batteries are fully charged. As an experiment when it drops to float turn the charger off and then on again. If the batteries are fully charged it will drop to float within  a very few minutes, if not it will stay in absorption for a while.

Unless you have changed the settings on a Victron away from adaptive charging it will drop into float at about 90% charged. You will have to restart the cycle every time or change the settings to fixed charging.

3 hours ago, Higgs said:

 

I think it would be a difficult decision to leave a battery charger on, not knowing when you'll be allowed to check on things. Would it not be possible to charge the batteries up and disconnect them? ?? Leaving them charged. 

 

My Victron charger was on from November to July, briefly visited the boat in March but couldn't go near it after that.

All my boats over the years have had a charger connected for the whole time they are on their moorings, only disconnected when we are cruising.

[David Mack]

17 hours ago, Loddon said:

 

All my boats over the years have had a charger connected for the whole time they are on their moorings, only disconnected when we are cruising.

 

Solar will do that for you without the need for power on the mooring, or any worries about power cuts, bollard tripping or galvanic corrosion.

[GUMPY]

34 minutes ago, David Mack said:

 

Solar will do that for you without the need for power on the mooring, or any worries about power cuts, bollard tripping or galvanic corrosion.

I now have 500w of solar as a backup, only once had the power trip out in 25 years on my previous mooring, resulting in flat batteries and a broken eberspacher, solar wouldn't have saved anything as there was a blanket of snow whilst I was away. Galvanic corrosion what's that? I have had an IT since 2006 and before that a GI