engine battery

2004 2500 Freightliner work van. 364,000 miles. For months I have had a electrical draw that draws down my battery. I have noticed a buzzing noise in the engine compartment when parked. Often battery will be dead in morning. My regular mechanic stated they could not figure out all the codes it...

My engine won't run. I was working inside my 2006 Sprinter last night with the interior light on for no more than 30 minutes. Took it for a drive an hour or 2 before with no issues. The lights and dash all still come on when I turn the key. The engine even starts but won't turn over and run...

How do I check/replace the battery for the engine. I believe it is under the driver's seat. 2008 Navion iQ. Thanks