There is a frequently used query on the solarev.ocpp_charge_sess table that follows this pattern:

SELECT *
FROM solarev.ocpp_charge_sess cs
WHERE cs.ended IS NULL
	AND cs.cp_id = $1
	AND cs.tx_id = $2

This results in a full table scan however, and the average query time is 18ms. An index on tx_id might be useful here to speed up the query.