Then do as I did. You cant really fix the root cause because its a combination of things, not least that those computers in the boot and their rf recievers, suck up power. As does the vans own mass of electrics. Those vans eat batteries and have high self discharge or rather self drain. So do the next best thing, fit a 50 to 80 watt solar panel on roof (clear silicone sealer and a few weights till it sets) , and run the wires behind the door rubber and down to the spare wheel area. Easy and hidden. Use a cheap ebay charge controller, set it to 13.3V and connect to any place you can find battery voltage behind that right hand plastic panel. With the key out. Then its always kept full for all but the darkest months, over winter. And where you live maybe adequate all year round?
Because jump starting may well work, but your battery is half discharged most of the time anyway even if it starts. So it wont last long making the problem worse, fast... It spirals because your battery capacity gets less, and so it goes flat faster. And the more its flat the more damage is done.
Fit NEW battery. On roof fit a quality flexi solar panel as below. My Odyssey sits at 13.30V all day every day. Except during the darkest 8 weeks in winter... Theres just not enough output at that time to keep up. From October end, to march end I raise volts to 14.0 as theres few hours and many long dark nights and days. I add a float charger at 13.6v to it for those few really dark weeks. It needs more volts in really cold weather anyway.
And no those small solar panels you stick on the windscreen wont work...