Here is a great post from Victron energy on optimising the BMV700 sync parameters ...

How to optimise the BMV-700 series sync parameters
​Does your BMV state of charge (SOC) synchronise too early or not detect a full charge? If so it is worth noting there are various settings for differing batteries and systems, to ensure your BMV works correctly. The default setup and settings are applicable for most situations, however the instructional video below shows you how to optimise the BMV-700 series synchronisation parameters for varying scenarios, to ensure the battery SOC read-out functions correctly. BMV-700 series models There are 3 model variants within the BMV series range: BMV-700 & BMV-702 (6.5- 95 VDC supply voltage range) and the BMV-700HS (60– 385 VDC supply voltage range). The principal function of the BMV series is to follow and indicate the state-of-charge of a battery. For the additional functionality that the BMV-702 provides, namely starter battery or temperature or mid-point voltage monitoring, please see the quick install guide. The video below gives clear instructions to ensure the BMV-700 series battery monitor synchronisation parameters are optimised.