Another battery/charging information source

[booster]

When I was digging around the Victron site looking for balancing information, I ran into a link to a book they offer on batteries and power systems. You can download a PDF or order a free hard copy.

https://www.victronenergy.com/upload...limited-EN.pdf

Very detailed and technical, but has much more information and reasons why than other places I have seen.

Areas I found really interesting were the explanations and reasoning behind selection of charge voltages, SOC, charge times, etc and how they are related to the compromised needed in real life. It is a good explanation of what you may have to accept in the real world is not what is the very best for the batteries, but can be made better of worse, just not great. Very detailed in explaining how the damage from absorption, float, and storage voltages make for different failure mechanisms. Same with high rate charging and temperature.

There is some noticeable pitch for the Victron products, especially towards the end, but that is to be expected, I think.

[booster]

Still reading and saw this, which is kind of appropriate with another thread that has some lost capacity batteries.

Batteries will in general reach their fully charged state, including equalization, during the absorption
charge or when float charged for a sufficiently long period of time.
If they have been used in partial state of discharge mode for some time, they will recover by:
- repetitive cycling and charging with the appropriate absorption voltage and time
- an absorption or float charge during a longer period of time
- a real equalization charge, see below.

I think this also backs up what Marko found with his batteries, which have gotten progressively better with repeated cycles to totally full.

[markopolo]

That PDF from Victron looks have great info. I scanned through it & plan to read it in full.

I think my batteries capacity has benefited from "or float charge during a longer period of time" from Boosters post above. They don't get cycled much. Propane fridge, furnace, water heater, LED lights and solar panels all make for light battery usage.

The risk of extended float charging would be drying out the batteries and corrosion of the positive plate grid as noted in the Victron PDF. Float voltage recommendation seem to vary from a high of 13.8V to 13.2V. 13.2V seems to be working out well for my batteries. I think both the dry out and corrosion risks are lessened with the lower voltage. The benefit of extended float charging is that it prevents capacity robbing, battery destroying sulphation (sulfation).

The folks at Rolls Battery - Battery Sulfation : Technical Support Desk - say that sulfation can start very quickly.

[booster]

The author does certainly seem to be a pusher of the lower float is better camp.

I also found it interesting that he contends that sulphation is not a forgone conclusion and that is the batteries are fully charger regularly, not necessarily all the time though, there won't be any sulphation. I have never heard that before that I remember.

It is also interesting that he appeared to be more concerned about oxidation from float than drying out. I was surprised at the statement that .3v higher float could double the oxidation rate. Most others are more concerned about drying out and sulphation.

[papab]

Great find!

[papab]

A couple things in there of interest.
In the table in section 2.5.5, he says that an AGM battery will survive 1 month in a short-circuited state.
In 2.5.7 he says to charge to 100% 'regularly, for example every 30 days'
Based upon my discussions with Lifeline tech support I don't think either of these are true for Lifeline/Concord batteries. They don't like partial state of charge and 30 days is too long.

Here's another good read on battery charging. He warns of the partial state of charge issue for AGM's, but he likes lifelines because they can be equalized.
AGM Batteries - Making The Choice | SailboatOwners.com Forums

[booster]

Originally Posted by papab

A couple things in there of interest.
In the table in section 2.5.5, he says that an AGM battery will survive 1 month in a short-circuited state.
In 2.5.7 he says to charge to 100% 'regularly, for example every 30 days'
Based upon my discussions with Lifeline tech support I don't think either of these are true for Lifeline/Concord batteries. They don't like partial state of charge and 30 days is too long.

Here's another good read on battery charging. He warns of the partial state of charge issue for AGM's, but he likes lifelines because they can be equalized.
AGM Batteries - Making The Choice | SailboatOwners.com Forums

I had noticed those statements also, and wondered about them. They aren't very well defined for one thing. "Survive" being shorted could be severely damaged, but still alive, which is likely, and the "once a month" is not all that bad if it is just one shallow discharge cycle, when compared to 30 discharge cycles. Lifeline says you can sit up to 90 days without charge, but they want you to start full. Of course, by 30 days you aren't full anymore, so who knows.

I think all the AGM recommendations are still works in progress. My guess is all the original recommendations for charging, storing, use, etc were based on lab tests. Now they are finding out the real world doesn't work in as controlled a way as the lab, so they are recommending modifications to the recommendations. Things like higher charge voltages, full charges based on number of cycles not time, higher amp charging for deep discharges, high voltage constant amp stage at end of charge cycle, all look like compensations for real world usage issues.

I have seen a definite drift away from the worrying about drying out AGM batteries to worrying about undercharging, probably because the manufacturers are seeing more undercharge damage than drying out damage. I can understand this, as most of the "smart" chargers will not charge batteries anywhere near full, but in the old constant voltage chargers, drying out was the issue.

I think it is best to look at all of the issues and try to fit best practice in the real world around them. Mostly this can be done with equipment, so it shouldn't really be a big inconvenience. Chargers and solar controllers that assure full charging are a big step. Just knowing how much time it takes and how often you need to get a full charge allows you to set your own risk/reward level. You will never duplicate the lab results, but you can make sure you don't duplicate the results that kill a battery bank in 6 months.