AGM Battery Question

[sv_naidia]

Hello Everyone,

I recently replaced my 2 house batteries on my E34T with Series 27 AGM's. My starting battery which is always isolated or if needed, joined to the house bank is also a series 27 AGM.

For those of you who have had success in using AGM's, how far do you allow the voltage to deplete before charging? Knowing AGM's do not like to be drawn to zero, it would be interesting to see what other folks here have experienced. On my old boat, I never used to let them go below 11vdc before charging but some have said that is way too conservative....

Thanks in advance for the input.

 

[Maine Sail]

You'd be wise to not draw them below 50% state of charge and charge them to full after each use, if you want long life out of them. If you don't have a battery monitor it would be a very wise investment. Voltage / open circuit voltage readings tell you little unless done properly.

Which brand of AGM are they?

These are all statements from Lifeline Battery one of the industry leader's in AGM technology.

“For maximum battery life, a battery must be recharged to 100% capacity. Recharging to less than 100% may result in premature battery failure.”

“For maximum battery life in cycling applications, do not discharge the battery bank below 50%.”

“Always use batteries of identical make, model and with the same manufacturing date.”

Lifeline AGM OCV /State of Charge:

12.8+ = 100%
12.5 = 75%
12.2 = 50%
11.9 = 25%
11.6 = 0%

11 volts OCV is not conservative it is below 0% state of charge...

 

[Stu Jackson]

...how far do you allow the voltage to deplete before charging? ...On my old boat, I never used to let them go below 11vdc before charging but some have said that is way too conservative....

I think you have the concept of charging backwards. You seem to think that the idea is to let them go down before you charge. That's not correct. Your approach should be: How do I keep them as full as possible before using them.

Of course, when using them, they will go down. But you should work out a regimen to get them back to charging as soon after you use them as you can. With AGMs this is more critical. But ALL batteries will have a longer life if you keep them topped up.

Another very good post by Maine Sail about AGMs is here: http://forums.catalina.sailboatowners.com/showthread.php?p=848465&highlight=darn agm

So, regardless of battery type, and even more extreme for AGMs, rethink your charging concepts.

 

[sv_naidia]

Interstate AGM's

You'd be wise to not draw them below 50% state of charge and charge them to full after each use, if you want long life out of them. If you don't have a battery monitor it would be a very wise investment. Voltage / open circuit voltage readings tell you little unless done properly.

Which brand of AGM are they?

These are all statements from Lifeline Battery one of the industry leader's in AGM technology.

“For maximum battery life, a battery must be recharged to 100% capacity. Recharging to less than 100% may result in premature battery failure.”

“For maximum battery life in cycling applications, do not discharge the battery bank below 50%.”

“Always use batteries of identical make, model and with the same manufacturing date.”

Lifeline AGM OCV /State of Charge:

12.8+ = 100%
12.5 = 75%
12.2 = 50%
11.9 = 25%
11.6 = 0%

11 volts OCV is not conservative it is below 0% state of charge...

Hi,

Thanks for your reply. I replaced the West Marine AGM's I had with Interstate Marine series 27's. Your info is useful.

 

[sv_naidia]

Charging

I think you have the concept of charging backwards. You seem to think that the idea is to let them go down before you charge. That's not correct. Your approach should be: How do I keep them as full as possible before using them.

Of course, when using them, they will go down. But you should work out a regimen to get them back to charging as soon after you use them as you can. With AGMs this is more critical. But ALL batteries will have a longer life if you keep them topped up.

Another very good post by Maine Sail about AGMs is here: http://forums.catalina.sailboatowners.com/showthread.php?p=848465&highlight=darn agm

So, regardless of battery type, and even more extreme for AGMs, rethink your charging concepts.

Hi Stu,

Thanks for your reply. I re read my original post and I guess I wasn't clear. I always begin with a fully charged bank. I am also diligent about recharging. Understanding longer life and load capacity at its best, my question was when..... this forum is always so helpful and I appreciate all the authorities on every topic imaginable.

Thanks again, Stu...

 

[Stu Jackson]

Good to hear, Ron. Quite often we are faced with folks who "start out with charged batteries" and think that's the norm. As "cruisers" we're faced with the challenge of dealing with "starting with depleted banks" and how to top them off. Enjoy.