The Tail Current, It, default parameter setting is wrong. The default is 4% of Battery Capacity in Amps. My battery is 1000Ah, so that is 40A. Or perhaps it is just incorrect for light discharges?
I noticed sometime ago, actually a few years now, that when charging the CE and SOC would suddenly jump to 0 and 100% respectively. I realised that this happened shortly after It reduced to the default 4%, ie 40A.
So, some real readings on our motor vessel a few days ago.
When we sailed the BMV602 showed CE - 54.4Ah, SOC 96%. I have a Smartguage, voltage based capacity, as well, and that was 94%. The 2% discrepancy is not unusual and largely caused by using high current draw items such as an electric kettle. Initial current from 24v alternators was 180A, but this quickly reduced below 80A.
24 mins later the charge rate was down to 40A. The 602 default It of 4%. 3 mins later Tc would have been met. Vc also met. So V602 would have suddenly shown CE 0.0 and SOC 100%.
The 602 would have shown the battery to be fully charged. But the parameters were actually CE - 30.7, SOC 97.9 and SG SOC 97%. The Victron defaults are suspect.
If this was used to stop charging, the battery would be undercharged and over time with similar repeated charging deteriorate.
After 58 mins the SG SOC was 100%. But 602 was still showing CE -15 and SOC 98.8%. The SG warns about SOC when charging as the charging voltage is above the “fully charged” voltage.
So relying on a voltage calculation isn’t perfect either.
After 2h 29 mins the 602 finally counted all the Ah back in and reached CE 0.0 and SOC 100%. This is affected by the choice of Charge Efficiency Factor. Peukert Exponent will also have an impact on the CE value. I haven’t changed the Victron default settings.
However, the It didn’t actually drop below the minimum 0.5% or 5A until 5h 38 min of alternator charging.
When I reckon the battery was properly fully charged.
I have reduced It to the minimum, upped Vc and Tc.
I’m not sure if I understand what you want to say.
If the default tail current doesn’t suit to your system you have to adjust it.
The BMV only knows and uses the parameter you enter.
The default is a starting point, on my 690Ah of quality AGM i have settled on a tail current of 0.8% from observation.
However, a set of basic flooded lead acid batteries charged at a high absorption voltage would never get below 2-3% tail current so having a default of 1% for those would be wrong for other reasons.
Lithium batteries are often charged to 4% tail current depending on manufacturer requirement.
Any default value is a compromise and will.not suit all conditions.