Has anyone attempted to charge a 75AH Pylontech battery, using a charge controller with adjustable voltage settings. Charging from a 125AH BSL battery. The BSL has higher voltage settings than a Pylontech. Any thoughts on this?

Just for interested persons I done a test and it seems to work ok because the BSL is a 16cell with higher voltage it can supply the Pylontech that is a 15cell that operates at a lower volrage. I will get a better quality charge controller because the one I'm using is not the best controller. The reason for testing this is to charge the BSL throug pv solar and than chargeing the pylontech from the BSL as a back up battery.

1 hour ago, Gerrie said:

The reason for testing this is to charge the BSL throug pv solar and than chargeing the pylontech from the BSL as a back up battery.

I would suggest using a dedicated a.c. trickle charger if you won't be using the Pylontech regularly. If you will be using it regularly, you should build a circuit that disconnects the battery from the BSL at the recommended maximum voltage. When the voltage of the BSL drops to that of the Pylontech, you should parallel it with the BSL. Note that you will probably burn some contacts and possibly blow up the Pylontech. 

8 hours ago, frivan said:

I would suggest using a dedicated a.c. trickle charger if you won't be using the Pylontech regularly

Currently I'm completely offgrid so an ac charger would mean converting dc to ac and ac to dc again, I'm not sure what the efficiency losses will be like, Currently I manually shut the inverter down from one battery and restart the inverter by manually switching over to the spare battery, probably about once a week.

1 minute ago, Gerrie said:

Currently I'm completely offgrid so an ac charger would mean converting dc to ac and ac to dc again, I'm not sure what the efficiency losses will be like, Currently I manually shut the inverter down from one battery and restart the inverter by manually switching over to the spare battery, probably about once a week.

I am guessing you have excess solar in the day, then the conversion losses don't matter. Are you switching over because you have cloudy days once a week, run big equipment once a week or are you testing the batteries? In my mind the Pylontech is fine to keep at 100% SoC for months.

1 minute ago, frivan said:

Are you switching over because you have cloudy days once a week,

Yes, mostly cloudy days late in afternoon, this make the BSL to drop to about 90% at sun set. I have about 25% excess solar during the day that goes wasted.

Have you thought of trading/selling the BSL for another Pylontech?

1 hour ago, frivan said:

Have you thought of trading/selling the BSL for another Pylontech

The plan is to get another BSL next year, the Pylontech will then go to another smaller installation. So for this coming winter I want to use the Pylontech just as backup.