Flooded,AGM or Gel deep cycle batteries 12volt

harold1946 wrote:

klutchdust wrote:
and adjusts the charge accordingly.

Hopefully he also recommended a multi-stage charger.

Isn't that what he said ?

harold1946 wrote:
I have seen discharge rates as high as 40%/month in new wet cell batteries.

Please tell us what brand of battery that was so we can stay away from them.

In 40+ years of dealing with wet cell batteries, that is the first and only claim I have ever seen of a self discharge rate anywhere near that bad in a "new" battery.

You are right that there is an inherent rate when new due to the chemistry and construction......which is pretty much constant over the useful life of the battery. It is the chemistry CHANGE mostly due to sulfation that makes the self discharge rate become worse over time.

klutchdust wrote:
I just got off the phone with the tech department at Parallax. He explained to me in great easy to understand detail what to do in my present situation.

I plan on upgrading my charger/converter to one that has temperature control that monitors the battery temperature and adjusts the charge accordingly.

It also features a boost mode if the battery requires it. I will then purchase 2 AGM batteries and be done with it.

Hopefully he also recommended a multi-stage charger.

Vulcan Rider wrote:

harold1946 wrote:

One of the advantages with AGMs is that if they are fully charged and disconnected the only self discharge 1-3%/month, where wet cells discharge from 10-30%/ month.

While this is absolutely true, your wet cell numbers are too high for a HEALTHY wet cell that is fully charged.

It's more like 5 to 7%.
Anything over about 15% a month is a good indicator of significant sulfation and impending failure.

Each wet cell battery manufacturer uses a lead - antimony alloy of their choosing. That alloy is what causes the self discharge, and can vary greatly. The higher the % of antimony the faster the discharge rate. I have seen discharge rates as high as 40%/month in new wet cell batteries.
Gel cell and AGM batteries use a lead - calcium alloy which greatly reduces the self discharge rate.

klutchdust wrote:
I just got off the phone with the tech department at Parallax. He explained to me in great easy to understand detail what to do in my present situation.

I plan on upgrading my charger/converter to one that has temperature control that monitors the battery temperature and adjusts the charge accordingly.

It also features a boost mode if the battery requires it. I will then purchase 2 AGM batteries and be done with it.

Our 8 year old 2000 watt Trip-Lite inverter/converter has a temperature sensor. I keep it sandwiched in between the pair of batteries held in-place with a strip of electrical tape. I have always wondered if it does any good, a feature you never know is working.

I just got off the phone with the tech department at Parallax. He explained to me in great easy to understand detail what to do in my present situation.

I plan on upgrading my charger/converter to one that has temperature control that monitors the battery temperature and adjusts the charge accordingly.

It also features a boost mode if the battery requires it. I will then purchase 2 AGM batteries and be done with it.

harold1946 wrote:

One of the advantages with AGMs is that if they are fully charged and disconnected the only self discharge 1-3%/month, where wet cells discharge from 10-30%/ month.

While this is absolutely true, your wet cell numbers are too high for a HEALTHY wet cell that is fully charged.

It's more like 5 to 7%.
Anything over about 15% a month is a good indicator of significant sulfation and impending failure.

The best charging voltage for AGM batteries depends on what the manufacturer recommends. For our batteries made by Odyssey, the best recommended bulk charging voltage is 14.7 volts. They did a cycle test of some batteries and found that 14.7 volts provided many more charging cycles compared to 14.2 volts. Up to more than twice as many cycles. Their comment is

"The message to be taken from this graph is clear – in deep cycling applications it is important to have the charge
voltage set at 14.4 – 15.0V. A nominal setting of 14.7V is a good choice, as shown by the test results.".

Our bulk charge voltage is 14.4V so we are in the preferred range. After bulk charging the voltage drops to 13.6, then 13.2 for float.

You can read this in their technical manual here, top of page 14.

EsoxLucius wrote:

harold1946 wrote:
It is best not to charge any battery to more than 13.8 volts unless de-sulfating or de-stratifying.

Say what? My batteries accept 14.7 volts for bulk and absorption charging, and 13.7 volts in float. Such generalizations do no one any good.

Its not a generalization, its a fact.
Read more carefully. Paul asked if his 13.6 volt charger would work and the answer is yes. That indicates to me he has a single stage charger, maximum output 13.6 volts.
If you do not believe fully charging a battery at 14.7 does any harm, give it a try.
Float charge is bringing them to a fully charged state. If 14.7 volts is used for float charging you risk thermal runaway on AGMs. Excessive gassing off of wet cells and total destruction of gel.

The AGM batteries we had in our motorhome so many years were specified to be floated at 13.5 volts to 13.8 volts .... as are the new AGM batteries that recently replaced them.

My AGM batteries get charged and floated most of the time by the same voltage ... 13.6 volts from the motorhome's stock single voltage converter. It just takes longer to charge them at 13.6 volts than it would using 14.X volts. I do charge them sometimes from the engine alternator when traveling between campsites, and they'll get fully charged from the alternator in 4 to 5 hours of driving, depending upon how discharged they were.

The main reason to use higher charging voltages is to speed up the charging process. I see a lot of discussion in these forums regarding possible reasons as to why using higher voltages (than 13.6 volts) is necessary for charging in order to get the longest life from AGM batteries, but I'm not convinced of any chemistry reason for this in everything I've read. If AGM batteries get fully charged at 13.6 volts, then it seems to me that they're as fully charged as they would be had one used 14.X volts for less time.

I wired an ammeter permanently into our RV's AGM battery bank circuit so I can tell at all times how much positive current is flowing into them (being charged) or how much negative current is flowing out of them (being drained). When that meter reads "zero" after so many hours of charging - whether at 13.6 volts or higher volts - then I assume that they're fully charged.

What is very important for AGM (and wet cell batteries) is that you get them back to a full charge after each use. Don't let them sit around too many days or weeks in a partially charged state ... there is a chemistry reason as to why this is hard on them.