You can check your battery’s charge level using a voltmeter. This is normally a function found on a multimeter; through the information provided by your battery charger/tender; or perhaps your campervan or motorhome is fitted with a permanent voltmeter in a display panel. Once you have your reading you can look it up on a state of charge table to determine the current level of charge (e.g. for a 12v battery, 100% charge would typically be 12.7v+ and anything below 12.4v, or 50%, would be considered low on charge).