Switching to AGM Batteries (Start)

[pugslyyy]

Interesting article. I had not realized that (some) newer vehicles have different charge profiles that you can change depending on the battery you are running. Good to know if you are swapping to AGM or gel and what to get the maximum benefit.

AGM or gel cell battery replacement is the same as flooded battery replacement.

True and False. While the installation of the *battery may be the same for the two battery styles, some vehicles require an extra step to tell the vehicle that the battery has been replaced. Newer GM vehicles have a Battery Sensor Module on the negative *battery cable. Ford has the Battery Monitoring System (BMS). Other manufacturers have similar systems. These systems require recalibration with a scan tool if the battery is replaced. If the system is not recalibrated, the alternator might overcharge the new battery and cause the battery to fail soon after replacement.

http://www.autocarepro.com/article/125726/Three_AGM_Gel_Cell_Battery_Myths.aspx

 

[DiploStrat]

One Minor Correction/Comment

The article makes the comment that AGM batteries like to be charged "low and slow." While AGM batteries want a lower charging voltage than conventional flooded wet batteries (typically 14.4v vs. 15v @ 20C) there are a few things to consider when installing into an older vehicle.

Battery manufacturers have upped the charging voltage specification from 13-14v to 14-15v across the board. While a modern AGM battery wants a lower voltage than a modern open cell battery, that voltage may still be higher than your older vehicle can produce because most older vehicles have 13v charging systems, not 14v.

So the first step is to test your vehicle's charging voltage. If it is lower than 14v, then you will have problems with any modern battery.

Lifeline AGM batteries, for example, want a charging voltage of about 14.4v @ 20C and a minimum charging current of .2C. They can take up to 5C. That is a LOT of current.

N.B. 1C = the 20 hour discharge rate of a battery, as in "100Ah." So a 100Ah Lifeline AGM battery needs a minimum bulk charge rate of 20A and can take up to 500A. Obviously, during the absorb/accept stage, this current will drop dramatically.

N.B.2 All of these voltages rise when the temperature drops, so by 40F a Lifeline AGM is looking for about 15v.