we put in a brand new battery about 2 months old but it drained already. this is about the 3rd time it has happened. the charging system is good. no engine check light. any suggestion???

 

Might want to give PD More details... Aftermarket electronics? HIDs? Radio? Something is grounded bad and causing a voltage drain.

 

yes, you have a drain, assuming your alternator is charging correctly, and the vast majority of drains are from some type of aftermarket add-on, like Shiryo correctly pointed out, an aftermarket stereo, HID's, etc.

bone stock LS400's do not tend to have any drains

the first step is to put a voltmeter across the battery with the engine at idle, to verify alternator performance, you should have at least 13.1V at idle and at least 13.6V at 2500rpm