I have dedicated jump boxes without all the doo dads...... 2 Schumachers and a Die Hard. Get the max amp you can. That 400 ain't much. Also make sure you take it and charge it every week or two to keep it at peak.
I have a Schumacher as well. I charged it once last season before we went on an extended trip a few hours away from home. It then sat on the boat for most of the year last year without being used and sat in our garage over the winter. Pulled it out yesterday to charge it up for the weekend camping trip, only took 5mins to charge to 100%!!!
I went with one that has the USB port for charging phones and other devices, as well as the air pump for blowing up trailer tires, footballs, volleyballs, etc while camping/boating. It works like a champ. Here it is:
