Many questions about charging a lead acid battery
Can't help with the chip/diode specifics, but here's some battery basics.

Each batt model has different specifications for Absorb voltage, Float voltage and endAmps, the tapering current point defining Full, at which voltage is allowed to drop from Absorb to Float.

I would not buy a battery where those specs are not available, as well as e.g. charts showing avg DoD impact on lifetime cycles, temperature vs discharge curves, etc.

But faced with an unknown, look for that data on similar batteries from more diligent vendors, and approximate is good enough.

To get a decent charge, current rate needs to also be high enough. Cheap lead can't accept more than .2C anyway, so for a 9Ah batt you should use at least an amp, but over 2A would be better for testing.

Your current rate and short charge time likely means you never got anywhere near Full, which shortens lifespan cycles.

So, just as an example:


Absorb 14.4V - 14.7V
Float Voltage = 13.8V - 14.1V
endAmps = .005C
Max Absorption Time = 12 Hours
or, Current change over 1 hour period of less than 0.05A
Temp Compensation = -.018V for every degree °C rise above 25C


So, discharge the battery to 50% SoC. If you don't have a proper discharger or battery monitor SoC gauge, a cheap Ah meter will do.

Set a power supply to 2-3A @14.7 max, measure V and A as SoC climbs during Bulk/CC stage you'll see V climb. When 14.7V is reached, probably less than 2 hours, that's now Absorb/CV stage, maybe 4-6 hours remaining to get all the way to 100% Full, not sure used to working with 300-800Ah banks.

You'll see amps dropping, the stop-charge spec is .005C, so for 9Ah that's 50mA.

But an old / worn / poor quality batt may not get there within the maximum 12 hours, so if you see the current just sitting, no longer dropping by over 50mA per hour, you can use that as your Full point.

Measure the actual SoC with precision if you can when the batt is new, at the 20-hour discharge rate down to 10.5V (0% SoC), will be a bit higher or lower than 9.0Ah.

From now on, if using different current or voltage rates can be used, that Ah capacity benchmark becomes your objective measure of 100% Full.

As the battery ages, the point where that capacity drops, that % aka State of Health, standard EoL is 80%.