It is an additional baterry placed under driver seat in my van. The battery has 80Ah and its purpose is to power fridge, auxiliary heating, DC/AC converter and other electronic gadgets like smartphone, camera, watch, etc. While the engine is turned off then the leasiure battery is totaly separated from main battery of the van. Therefore, I can be calm about the condition of the main battery. I mean, even if the leasiure battery is dead then the main battery will be sill in good condition and I will be able to start engine. All the time the leasiure battery is charged by solar panels (of course during a day), moreover is is charged by alternator while the engine is turned on.