AGM Battery Charging - Temperature Dependent

Max Dunn — Fri, 23 May 2008 19:00:00 -0700

As we have seem, the biggest per mile cost of running an electric vehicle is not the electricity, it is the battery depletion. So it is important to maximize the life of your batteries. One trick that works with all battery techologies is to take short trips and recharge after each one. By minimizing your depth of discharge (DOD) you will maximize the total energy that the batteries will deliver over their life.

Another very important factor is to charge the batteries correctly. Especially for sealed lead-acid batteries like gel or AGM, correct charging is critical. Deka states that if their batteries are continuously charged with a voltage that is only 0.70 volts over the proper charging voltage, it will reduce the battery life by 60 percent! This is because if sealed batteries are overcharged, they will dry out and there is no way to replace the lost moisture. It is likely that all sealed lead-acid batteries will suffer from this, not just Deka batteries.

Here is the kicker: the proper charging voltage varies depending on the temperature. It ranges from 15.10 volts when it is below 40 degrees 13.60 volts when it is above 120 degrees. And it is not good enough to just measure the air temperature, instead it is important to measure the temperature of each battery since they will often be warmer than the outside air.

So unless your charger or BMS has a temperature probe on each battery, it is almost guaranteed that the batteries are not being charged correctly and that their potential life span will be reduced.

"AGM Battery Charging - Temperature Dependent" by Lawrence

Mon, 09 Feb 2009 21:53:50 -0800

The Deka pdf file that you have a link to has a lot of good information, but the most important is probably on page 11 where the temperature/peak charge voltages are listed (both for bulk and float levels).

About a half a year ago a solar installer had actually referred me to that page.

It is depressing to think that so many people (myself included) have been misled by the simplistic or plain inaccurate information that has been disseminated about peak voltage levels . . .

However, another important factor that I have discovered is that neither of my charge controllers (one my Xantrex, and the other by Blue Sky) change the voltage much due to varying temperature, despite both having temperature sensors connected (and both affixed securely to their respective battery banks) . . .

I don’t think this is unique to these charge controllers. There needs to be a critical look at how little charge controllers with “temperature sensors” actually alter the voltage.

While I respect the solar publications out there, such as Home Power, I don’t expect them to really say much about this under-reported issue, or report about it in their reviews . . .

What we need is the kind of consumer reporting by those that not only know their stuff (as in HomePower), but are not afraid to talk about it candidly, even when reputable manufacturers make mistakes like this.

Eschew Obfuscation: AGM Battery Charging - Temperature Dependent

AGM Battery Charging - Temperature Dependent

"AGM Battery Charging - Temperature Dependent" by Lawrence