Hello,

I've replaced my 110AH battery with a 100AH AGM battery. However, the highest AGM capacity that can be registered is 90AH. My choices are therefore to register the battery as a 110AH non-AGM (like my old one), or a 90AH AGM. I decided on the latter since I figure it's safer to under-charge than to over-charge, and it's important for the charging system to know that the battery is AGM. Seems to be working fine so far. Did I make the right choice?

Thanks,
cinergi

 

+1. AGM batteries have a different charging regiment than a FLA battery. AGMs are voltage sensitive and will not tolerate being charged above 14.7v, even in cold weather. They will also accept a highest charge rate than FLA batteries. I have used AGM batteries on our sailboat for the past 15 years with great success, with a smart voltage regulator, which allows a much faster charging regiment during the bulk acceptance period, 50% to 80% .
In your case, you are better undercharging and weekly hitting it with a smart charger.

 

You did the right thing choosing 90AH AGM.

 

Cool, thanks for the confirmation jtbgonesailing and twh!

 

Hmm... I found out today that my new battery is not actually AGM, I made a mistake. Needless to say, I will need to re-code it as non-AGM, but should I use the 90AH or 110AH capacity? What is the impact of selecting 110AH? I'm concerned that selecting 90 would result in the battery not being fully charged?

Thanks
cinergi

 

Set it to the closet thing in the available options.

 

That's the problem: the available options are 90AH or 110AH, both of which are exactly 10AH off from the battery's actual capacity (100AH). Makes the choice more difficult :-). So the choices are either to chronically undercharge or overcharge the battery. I'm currently leaning towards the former (90AH) because while it will result in reduced battery capacity, I think it's probably more harmful in the long run to overcharge it. Opinions?

Thanks,
cinergi

 

I would set it for the 110AH. You're only talking a 10 % overstating of the capacity. Don't forget to reset to the FLA battery setting from AGM.

 

Thanks; yes, I will reset it to FLA and re-register it.

-cinergi

 

I don't think setting it for either 90AH or 110AH is going to matter really. I might be inclined to choose 90, but really either will be fine.