Topics

AGM Batteries (was: Battery pack replacement at 4 Years boating)


 

Congrats on the new ride, David. :o) I sure liked Mary's Roadtrek, and I know she misses it too.

AGMs are nice, and I'd like to use one in my little MyPod trailer, but can the plugin charger be set to charge AGMs right? I'll have to do some research... So far I haven't had the little thing out even once this year. <sigh> For your Sportsmobile, will the engine-driven charging system treat AGMs right? Before springing for those expensive batteries both of us should do our research. <g>

I don't worry about it in Lazy Jack because I've got a surfeit of battery capacity, and I think the trouble with using a charging system set up for flooded cell batteries on AGMs is that you don't get the most out of the batteries, rather than damaging them. When I charge up at home I use a smart charger that can be set for AGMs. The starter battery is quite old, and the house battery is several years old, and they seem to be doing fine. I got them from a small local battery shop that used to to actually rebuild, and maybe even build, batteries back when they came in rubber cases! <g> I don't know where they get their new batteries nowadays...

In the other direction... The 24-volt charger that came with Tuffy is intended for electric wheelchair batteries. I know that Laura McCallum's wheelchairs have used AGMs for quite a while. Does using an AGM charger on flooded cell batteries do them any harm?

On 11/9/2020 7:57 AM, Thorne wrote:
...
Somewhat inspired by Master Kohnen's lady's Sprinter RV at Paulina years ago, we've managed to pick up a high-mileage 2011 short wheelbase Sportsmobile Sprinter Class B and have already used it to tow Goblin up to Humboldt plus a primitive camping trip up Hwy 4 near the crest of the Sierras.
...
The house batteries are ancient and need replacement, so once that's done we'll have more juice and might be able to take a shower without having to run the diesel for 20 minutes.
We don't have Bi-Mart down here, but do you have any other recommendations for 100 Ah AGM house batteries for a small RV?
...
--
John <jkohnen@boat-links.com>
Women and cats will do as they please, and men and dogs should relax and get used to the idea. (Robert A. Heinlein)
--
This email has been checked for viruses by AVG.
https://www.avg.com


johnacord
 

Here are the voltages listed in my battery charger (Xantrex Truecharge - temperature compensated) :

Absorption voltage: @ 25 °C (77 °F) { battery temp, not ambient! }

Flooded  14.4 ±0.1
AGM      14.3 ±0.1
Float Voltage:
Flooded  13.5 ±0.1
AGM      13.4 ±0.1

Of course all this depends on your desire for battery life. 

Personally, I float at lower voltages depending on application.  I prefer to monitor voltage and recharge, stopping the charge when the battery is full based on charge current.

For most of our usage in recreational boating there is no need to float unless the battery system unless it's needed for standby such as boat left in the water for extended time with the need for a bilge pump exists for safety.

John Acord


Myles Twete
 

These settings work great for batteries that haven’t been sulfated at all.  Newer and well-treated batteries will charge and receive their near-rated charge levels with that type of charge regime.  However, overheat the batteries, dry them out or leave them without recharging for long enough and sulfation happens.  After that, the batteries will not charge fully and may not accept charge at all without radically changing the charge profile.

Sometimes this means applying up to 100vDC to a 12v battery just to get some current to flow, then carefully monitoring for voltage, current, heat, smell.  Once current starts flowing, the voltage drops quickly, however it doesn’t drop into the usual “rising voltage with charge current” curve.  Rather, the voltage “drops with charge current” over time.  And this makes sense because you’re dealing with a battery that has developed high internal resistance and as it warms up and recombines sulfated material, the internal resistance keeps dropping.  Charge algorithms are not designed to deal with this as far as I understand.  Maybe the only ones that come close are ones that have a high freq/high volt “pulsed” mode for desulfating.  But even then, in my experience, once a battery gets into this state, it seems they never get back into the usual charge curve.  And so these chargers/maintainers really don’t help and indeed do the wrong thing.  And that’s too bad, because the only way to keep these batteries healthy and alive is quite a bit of manual work and close observation to avoid dangerous overcharge/overtemp situations.  The alternative is to accept drastically low capacity or to throw the batteries out.

 

Anyway, enough on this I suppose.  Ditch lead-acid and you won’t have to deal with this anymore J .

 

-MT

 

From: oregoncoots@groups.io [mailto:oregoncoots@groups.io] On Behalf Of johnacord
Sent: Thursday, November 12, 2020 10:19 AM
To: oregoncoots@groups.io
Subject: Re: [oregoncoots] AGM Batteries (was: Battery pack replacement at 4 Years boating)

 

Here are the voltages listed in my battery charger (Xantrex Truecharge - temperature compensated) :

Absorption voltage: @ 25 °C (77 °F) { battery temp, not ambient! }

Flooded  14.4 ±0.1
AGM      14.3 ±0.1
Float Voltage:
Flooded  13.5 ±0.1
AGM      13.4 ±0.1

Of course all this depends on your desire for battery life. 

Personally, I float at lower voltages depending on application.  I prefer to monitor voltage and recharge, stopping the charge when the battery is full based on charge current.

For most of our usage in recreational boating there is no need to float unless the battery system unless it's needed for standby such as boat left in the water for extended time with the need for a bilge pump exists for safety.

John Acord