agm battery charge issue

It is normal for the battery voltage to rise during the absorption stage while amps taper. This occurs at different SOCs depending on the charging rate. You could be seeing the Absorption Stage starting earlier than you expected.

If the charging rate is with high amps you can have voltage drop between charger and battery so the battery voltage is lower than the charger's. As amps taper this difference in voltage becomes less as battery voltage rises.

Some PDs are not very good at constant amps in the Bulk Stage for whatever reason (Salvo used to complain about that with graphs to show it---however one guy here showed his graph where his did constant amps ok)

And as you note, with chargers it is loads first battery gets what amps are left over, so you might have had a load come on for a while that you were not aware of.

Not likely anything wrong with the AGM without more evidence IMO.

i think you missed what i said. the voltage is not rising above 13.6 yet the amperage is tapering.

the meter output of the PD is confirmed 14.4 during this.

there are no other loads, everything is off.

AGM's are Lead Acid. same as Flooded wet. Only more expensive and a few other things I won't bother with.

The PD tapers off when recharging Lead Acid batteries..
Ideally a 9245 would push 45 amps till it's like 90% then taper off rapidly but many people have shown that's not how it works.. It tapers off almost from the instant it starts.. Now.. as it happens I know why it does that but. Beyond this post.. And the folks who did the testing explain it rather well.

Here is part of it
Charger (PD9245)------ Wire----(Also known as a low value resistor)------- Battery.

As the battery charges the difference in voltages between the PD-9245 and the battery is reduced. as current = Voltage/Resistance. the wire leads cause (both inside and outside the converter) cause the charge rate to slow.

NOTE that the only convrters that do not do this are very expensive with "Remote Sense" leads (two sets of leads that connect to the battery one heavy (Charge) and one light weight (Sense) the Sense leads read the voltage AT THE BATTERY.

I've never seen one save on paper.

Source: Other threads in this very collection of Forums.
I do not have links.

This is what the salesman says happens: https://www.progressivedyn.com/rv/charge-wizard/

Alas I could not quickly find a link to what does happen.
But it's not square corners. it's more a smooth curve.

As I said. it was heavily discussed on one of the boards here. a few years back.

LittleBill wrote:
i think you missed what i said. the voltage is not the meter output of the PD is confirmed 14.4 during this.

Are you sure that it's measuring the actual output voltage right now, or is that just the voltage that your PD is set to terminate the charge at?

If the PD output is 14.4 and the battery terminals are 13.6 as measured by the same voltmeter.... there is resistance in the connection between the two. Could be the wire, a connection, fuse, breaker, switch, relay etc. Keep poking along the path until the differential is found. Clean, replace, repair or adjust that item. Some difference might be normal but 0.8 volt seems big at less than 45 amps.

And yes if the voltage on the battery terminals is just 13.6 volts the amps will be tapering at about 70%+ charged.

time2roll wrote:
If the PD output is 14.4 and the battery terminals are 13.6 as measured by the same voltmeter.... there is resistance in the connection between the two. Could be the wire, a connection, fuse, breaker, switch, relay etc. Keep poking along the path until the differential is found. Clean, replace, repair or adjust that item. Some difference might be normal but 0.8 volt seems big at less than 45 amps.

if that was the case how come when i put a load on it, it drops to 12.8 and the full 48 amps from the charger is going into the battery at 570w vs 198w at 13.6 plus whatever amps equals that

LittleBill wrote:
if that was the case how come when i put a load on it, it drops to 12.8 and the full 48 amps from the charger is going into the battery at 570w vs 198w at 13.6 plus whatever amps equals that

Because the drop is 0.8 volts. When the battery is pushed down to 12.8 the converter is pushed down to 13.6 (or at least well below 14.4) and goes to full amps.

time2roll wrote:

LittleBill wrote:
if that was the case how come when i put a load on it, it drops to 12.8 and the full 48 amps from the charger is going into the battery at 570w vs 198w at 13.6 plus whatever amps equals that

Because the drop is 0.8 volts. When the battery is pushed down to 12.8 the converter is pushed down to 13.6 (or at least well below 14.4) and goes to full amps.

yes but the v drop changes depending on amperage, it was doing 10 amps at 14.1. v drop doesn't remain static.

As stated the wire is to small and/or to long for optimal charging. AND this can include the negative wire.

The 48A from the charger first goes to the loads which is 48-14A=34A and 14A into the battery from your numbers.

You can also check for the PD recommended wire size per the distance and compare that to your wire size. And as stated the connectors etc could also be part of the problem.

BTW If your OEM charger has been replaced the wiring should be a big red flag. :R :h