The recent discussion about solar-powered float chargers has reminded me
of an issue that I've yet to understand or resolve...
I have a Battery Minder 12248 (12V 2/4/8A) charger/de-sulfator with
temperature compensation sensor. While I've never been able to
appreciably restore a dead UPS battery using the de-sulfation mode, it
seems to work fine as a slow charger. It has several modes -- gel-cell,
AGM or flooded -- which, near as I can tell, adjusts the threshold
voltage at which the charger switches from bulk-charge mode to
float-charge/de-sulfation mode.
Every 12V battery that I've ever connected to the charger, even the old
AGM batteries taken out of my UPS units, eventually reached the
threshold voltage and switched over to float mode (usually within 30-45
minutes for a nearly-fully-charged battery). Except one.
About 2 years ago I installed an Interstate battery from Costco (size
27F, 890CA, 710CCA) in my truck. It's a flooded battery and if I
understand Interstate's spec correctly, its capacity works out to around
100Ah. The battery has a resting voltage of 12.6V so it doesn't appear
to have any shorted cells and has no trouble starting my truck. So it
seems to be a normally healthy battery, right?
Thing is...I've never seen my charger go into float mode when connected
to this battery even when it was nearly new. With the recent pandemic
stay-at-home orders, yesterday I decided to connect my truck to the
charger to stave off parasitic drain (measured to be 20-30mA) that may
have accumulated over the past week of inactivity. I'm currently at 16
hours (@4A) and it still seems to be in bulk-charging mode. I have
difficulty believing that the battery needed 50+ Ah.
So what's going on here? This is the only battery that I've come across
that behaves like this.
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