Switching from lead to AGM, anything to keep in mind?

[PatrickG]

Hi all, sorry if this is a regular question - I searched the archives but did not find an answer on it. So we are just now switching from 5 12V/100Ah Exide Excell lead batteries, to 5 12V/110Ah Victron Energy AGMs.

My question is: can I just remove the old batteries, plug the new ones in, adjust my battery monitor to 550 instead of 500 Ah, and I'm good to go? Or is there more that needs to be adjusted on the charging side?

Besides the 75 amp alternator on our Volvo Penta MD22 engine, we also have a 25 amp built in prop charger, a Tecsup Tecpro Charger Evolution II 25 amp battery charger that charges from shore power (it's an original from the 90s I believe), and two Victron regulators that come from our solar and wind respectively.

Our current lead batteries have usually charged up to just under 14.4 V, then when charged have run at around 12.7 V - all totally normal. These sound like the same levels recommended by Victron for the AGMs, but I want to make sure I'm not missing something.

All advice much appreciated. I'm so excited about these new "maintenance free" batteries, and want to see that they last a long time!

Cheers,
Patrick

[a64pilot]

Have you bought the AGM's yet?
Do some reading, if you have the room, the golf cart batteries may, depending on your usage be a better choice.
Some people like me don't have much of a choice as our battery boxes won't accept the golf cart batteries.
But to answer your question, the charge profiles for an AGM is usually slightly different than a flooded cell battery. I assume flooded cell is what you meant by lead?

[Vasco]

Originally Posted by a64pilot

Have you bought the AGM's yet?
Do some reading, if you have the room, the golf cart batteries may, depending on your usage be a better choice.
Some people like me don't have much of a choice as our battery boxes won't accept the golf cart batteries.
But to answer your question, the charge profiles for an AGM is usually slightly different than a flooded cell battery. I assume flooded cell is what you meant by lead?

I went to AGMs a few years ago. They lasted two seasons. Unless you can fully charge them frequently, AGMs are not the way to go for a cruising boat. I'm back to flooded now. Lots of posts on this issue. Do a search.

[PatrickG]

Hi guys, thanks for the input. The batteries are bought and sitting in my cockpit right now. I bought them on the back of the experience of some tropical cruising friends who have them and love them. Sailed 8 years on their last set.

What would be great is further advice on the above question: do I need to make other adjustments to my charging system? And (oh boy) if so, any further experiences on doing that? Many thanks!

Cheers,
Patrick

[PatrickG]

PS this is the current battery type I've had: Exide 249se EB1004 Car Battery:Amazon.co.uk:Car & Motorbike

[a64pilot]

I'm not familiar with your chargers, Ideally absorption time and voltage is adjustable as well as float voltage.
Get with the battery manufacturer and find out at least what they recommend for absorption and float voltage and ensure that is either adjusted to their recommendations or is very close to their recommendations, then ensure the voltage as measured at the battery are close.
For example my old charger was fine, but the long and undersized wiring to to batteries dropped the float voltage to just above 12V, so while the charger was OK, the poor installation made it un-acceptable.

From my limited understanding AGM's do not tolerate partial charging nearly as well as a flooded battery will, and to charge to 100% is difficult, but necessary for a long life out of AGM's

[AfterHoursNLCT]

Originally Posted by Vasco

I went to AGMs a few years ago. They lasted two seasons. Unless you can fully charge them frequently, AGMs are not the way to go for a cruising boat. I'm back to flooded now. Lots of posts on this issue. Do a search.

My neighbors on the dock had EXACTLY the same results and have switched back to flooded lead/acid...

[SimonV]

You really need to increase your alternator size or reduce your bank into 2 separate banks or you will burn out your Alternator or have premature battery failure.

[AfterHoursNLCT]

Originally Posted by PatrickG

What would be great is further advice on the above question: do I need to make other adjustments to my charging system? And (oh boy) if so, any further experiences on doing that? Many thanks!

Cheers,
Patrick

I have a good article on my boat computer that I will post a link to when I get back there later today. Has all the information that you are looking for.

[Sandero]

I have 2 8D agms and a couple of solar panels and a high 100 amp alternator w/ a smart regulator... on a mooring and they are always topped up and work a charm. No maintenance and plenty of power.

[sailjumanji]

Patrick,

Earlier this year, I replaced the three original-equipment Deka 105 amp-hr AGM batteries on my catamaran. They were 12 yrs old when they finally crapped out. I replaced them with the same batteries. They were kept charged by both a solar MPPT controller, and a three-stage shore power charger. I didn't read the referenced "short life AGM" article, but just want to say my experience has been quite different.

Get a manual for your chargers. From what I remember, the charge level for AGM's is different than flooded cells. It was easy to reset.

[PatrickG]

Originally Posted by SimonV

You really need to increase your alternator size or reduce your bank into 2 separate banks or you will burn out your Alternator or have premature battery failure.

Hi SimonV, can you please elaborate on that? Why would a 75A alternator burn out, when it was worked fine with 500 Ah of batteries, when just moving up to 550Ah total? One note here: I'm not planning on discharging these batteries more than 50% max ever. Is there some reason why the AGM batteries specifically could put too heavy a load on the alternator?

[PatrickG]

Thanks all for the further input - great to hear not all AGM experiences have been bad - AfterHoursNLCT would be super to read that article!

So I talked with Victron this afternoon and they were very helpful. They specified the float voltage at 13.8V and the absorption at 14.4V (they also talked about a "charge current" limit of 10-20%, which was a bit more mysterious, hmm...). I did not have a manual for that original battery charger, 18 years old, so I talked to the Tecsup folks (so lucky we live in the age of Internet and mobile phones) who immediately mailed me a manual. And lo and behold, while the charger is currently set to a different setting for the flooded lead batteries, and it predates the widespread use of AGM batteries, it does have one which perfectly matches the new batteries' specs. Great.

So now I'm going to check ditto for my solar and wind regulators.

Which just leaves the engine alternator, and the sail drive generator (which looks and acts very much like an alternator).

Follow-on question - does anyone have any idea if it's possible or necessary to adjust the float voltage coming out of an alternator like that? They don't seem so very adjustable. Or do they run on a basic one-size fits all approach?

[sailjumanji]

My guess is that alternator is not adjustable. But I am only running twin 9.9 hp Yamahas, so alternators not that big.

One thing I did want to pass along regarding the AGM's is that someone told me - or some place I read - that they need to be brought back to full charge at least once per week. Maybe someone else can back me up on that. The discussion was regarding whether the two solar panels I have could run the watermaker for a few hours and still have enough daylight left to get the batteries back up to full.

My AGM's might have lasted so long because it was rare that they didn't get back to full charge each day. At the dock, there is a 3-stage battery charger that does the trick. At anchor, our situation is that usually around noontime the two solar panels have the batteries back to full and on trickle only. We have a Blue Sky three-stage MPPT controller. FYI

[Russ]

For what it is worth my AGM''s (1,000 amps worth) lasted SEVEN Years. granted I am at a dock 4 months of the year when I leave sunny FL for not so sunny VT in the summer. That said, Flooded batts are fine and cheap IF you have the time and presence of mind to refill the water and not kill a cell . They are by comparison high maintenance.
For me leaving them unattended for 4 months was a deal breaker when my original lead acids died.
Also remember to change the batt type on your charger, AGM's don't tolerate Lead acid charging parameters. Russ