[Al Skierkiewicz]

Tom,
I looked over your data and it is pretty much what you should expect to see. There are a few issues in the data. Your calculated battery resistance is flawed since it does not take into account the output impedance of the charger. The actual resistance goes down as the battery charges and is normally around 11 mOhms. It is normal for the current to go down as the voltage goes up simply because of the difference in charge voltage compared to battery terminal voltage. It is quite common for lead acid batteries to be charged with a constant voltage style charger. With that type of charger, the terminal voltage is low when the charge current is high. It rises as the battery becomes charged because lead acid battery terminal voltage rises with charging. As that is the case the only way to get the battery to take any current during charge is to force the charger to a higher voltage than the battery. Another charachteristic of lead acid cells is that when they reach full charge, any additional current forced into the battery is given up as heat. Since the charger is capable of a higher voltage than the battery, this will be the case unless the charger is smart enough to turn off when it senses the battery is at full charge. I am guessing the time scale is reversed in your graphs as the graphs represent typical charge and terminal voltage for these batteries. Nice work and it represents quite a bit of time commitment to bring this data to the group. Note that there is also a difference in starting current and this likely due to the different discharge conditions on the batteries you were testing. If I can figure a way to include this in my electrical presentation, can I use some of your data?
What may be at issue here is the difference between gel cell technology and AGM which is slightly different construction but uses the same chemistry. The suggested max charge current on the MK sheet for our battery 5.4 amps. The supplied charger is designed to output up to 6 amps. I wouldn't think that would be a problem but time will tell. I have given the MK rep all the data on the chargers teams were given over the past few years. He has not indicated a problem yet but others are still investigating the issue.