We strongly recommend the use of an external battery monitor with all, but especially lithium chemistry, batteries. The flat voltage curve of lithium means that voltage cannot be used as an indicator of SOC (unlike the resting voltage of a lead acid battery). Even batteries which have an integrated BMS which communicates via Bluetooth with a Smartphone app, will benefit from the more accurate readings gathered by a Victron BMV700/702/712 or a Victron Smartshunt. In addition, the BMV712 and Smartshunt can be used in a VE.smart Bluetooth network to help provide MPPTs with accurate voltage data, direct from the battery terminals.