Battery Charging

[pm6041141]

I have been trying to charge some Cyclon X-Cell SLA batteries. well, a bank of 6 actually, using a constant voltage charge profile. Since the batteries are used but known to be good, the charge controller was me. I setup two multimeters for current and voltage and applied 13.7v as the datasheet says. The current went from 20mA to 2.8A over the course of several hours of charging. This is opposite of what I expected. I thought that as the battery bank charged less current would flow into the batteries. Understandably the batteries became warmer as the larger current flowed. The bank is measuring a no load voltage of ~12v now, so they are getting charged. I have yet to do a capacity test. Am I missing something here?

Q2: I tried hooking up the bank to a "motorcycle battery charger" before the above experiment but the charger would not recognize that it was connected to my battery pack and refused to turn on. It did turn on for a motorcycle battery however. Any thoughts on why that may be?

[Entropy]

"used but known to be good" - When were they last used? If they were stored in a partial discharge state they may be BANNED, which might explain the initial low current. (the fact that it rose reasonably fast says that fortunately if the cause was sulfation, it wasn't too bad.)

[pm6041141]

Yeah, they have been in storage for a couple years I would guess. Just checked the datasheet and the self discharge rate for 25C is ~600 days. So, maybe it was sulfation. Perhaps I am being paranoid about the current increasing. Looking at the datasheet the current I measured (the final ~2.8A) is about right for these cells. I will charge again today while keeping an eye on them to see what happens.