Observations and speculation of 12v-battery charging system

[geomars]

The Victron Smartshunt internall stores its measurements of battery voltage, current in/out, and cumulative state of charge (independent of voltage). Whenever I’m curious, I connect my phone by Bluetooth and view plots of the measurements.
However, since changing the battery to an Odyssey performance series AGM, the battery consistently shows a good state of charge (typically above 85% even after not driving for a week), so I don’t check as frequently now.

 

[ultane]

The Victron Smartshunt internall stores its measurements of battery voltage, current in/out, and cumulative state of charge (independent of voltage). Whenever I’m curious, I connect my phone by Bluetooth and view plots of the measurements.
However, since changing the battery to an Odyssey performance series AGM, the battery consistently shows a good state of charge (typically above 85% even after not driving for a week), so I don’t check as frequently now.

Is your AGM ever fully charged? Ever???

 

[Mopper]

I keep my OBDII reader in the vehicle yes, and my phone (with Carista) usually gets in when I do. No, I don't keep it running, but plug in when curiosity gets the better of me.

Thanks ... it just became clear that my tablet is a present-day equivalent of cheater-glasses... I'll install on my phone and stick the interface in one of the side compartments around the battery deck.

 

[geomars]

Is your AGM ever fully charged? Ever???

There were 4 times in the last 7 weeks when the Smartshunt reported 100% State of Charge (SoC), and a few more times when it reported 98-99%. For comparison, I cross-checked SoC with battery voltage (after battery had rested 6 hours or more). The chart in the owners manual for my Odyssey performance AGM shows a fully charged battery has 12.84v. I measured resting voltages of 12.7-12.8v, corresponding to 90-97% SoC. I didn't measure all of them, so I can't say for certain that none reached the fully charged value of 12.84v.

So the short answer is that there have been times in the past 47 days when the Smartshunt reported 100% SoC based on summing inputs and outputs, whereas battery resting voltage indicated a SoC a few percent less. My hunch is that the small phantom drain during the 6 hours of "resting" can explain only a small part of the difference.

 

[D-mac]

However, since changing the battery to an Odyssey performance series AGM, the battery consistently shows a good state of charge (typically above 85% even after not driving for a week), so I don’t check as frequently now.

Careful, you're echoing what Big Battery has been telling us for decades that aftermarket AGM batteries can be safely charged with OEM 12v charging systems, just like flooded or sealed lead acid 12v batteries .

 

[geomars]

I’m just reporting what the measurements are. I have no data on battery life.

 

[basicxj]

There are AGM batteries that have similar voltage specs (resting and maximum charge) to OEM batteries, and there are AGM batteries that are capable of higher voltages when fully charged. It is the latter that likely will not reach full state of charge through the vehicle’s charging system alone. If you need that higher voltage and want to optimize battery life, avoiding partial state of charge for extended periods by topping off with a charger will help.

I had a Northstar and an Odyssey that needed periodic top ups (previous vehicle), but I also had a good amount of load on those batteries too.

 

[basicxj]

OEM battery today:

^^ system “Ready”

^^ accessory mode

This was after a number of short trips, the last being a ten minute drive. I would expect voltage to drop after being shut off for a while.

When I get my 2 channel dash cam in, I expect I’ll need to upgrade the 12V battery for extended parking mode, or at the least run a back up battery for the cam.