Is it safe to regularly (every night) drain a lifepo battery having internal BMS by running a 12V device? Or does external Victron BMS add something to the system? For AC output I have Multiplus II which can protect battery, but for 12V only a fuse block.
External BMS adds nothing if the battery has an internal one. They may not work well together, either.
Make sure the battery is sized to handle the overnight loads, but it's safe to leave them on. Worst case is the battery's BMS cuts the supply.
Victron BMS's are for Victron smart batteries, they aren't intended for any other purpose.
@pekkaj For AC output I have Multiplus II which can protect battery, but for 12V only a fuse block.
For the multi, please ensure that you set its low voltage cutout to shut the multi down before the battery is discharged and the BMS disengages the battery.
Likewise for the other 12v loads, use a Battery Protect (or something similar) to cut power before the battery is empty.
Oh, sorry I mixed up Battery Protect with BMS, so they are different thing. So I should use Battery Protect for 12V output even with battery build-in BMS?
@pekkaj you are better off for the loads to be disconnected from the battery, before the BMS cuts all loads and chargers due to low voltage.
Waking up a battery when the BMS has shut down requires extra effort.
What procedures does your battery require to re-enable charging?
I found the manual, so it seems that recharge is enabled without any procedure: https://www.suomenakut.fi/storage/product_files/5/217305-TB12200_37eb50f171eaa10ba8aacdd46101e852.pdf
Post a picture of what you purchased. People here will be able to identify and link you to the right manual or product to protect your battery from discharging too much with DC loads.
