sansa clip zip low battery life

[mike rowcosm]

Everything works great on my new rockboxed sansa 8gb clip zip with 64 gb sd card, except i'm only getting around 5-6 hours max battery life.  I made sure it was fully charged, always power off when not in use, and don't have the equalizer on.  I checked some other options such as crossfeed and crossfade (which supposedly diminish battery life) and these were also set to off.  For sound settings, the bass is set to 10db, and treble is at 4db,  and replay gain is set to 'track gain when shuffling'. There's about 45 gb worth of music altogether on the player.
Before I installed rockbox the battery life on the player was normal (actually noticeably better than my other identical clip zip which is two years old).  So i'm wondering if there's any settings i'm unaware of which would optimize battery life, or whether the battery drain is due to the 64 gb card being used on this player (which normally supports a max 32 gb card with sansa firmware).  Thanks

[saratoga]

Could be a bad sd card.  Try a battery bench without the card.

[mike rowcosm]

thanks--i'll try that.  I'm wondering if the card was properly formatted, as I used the quick format feature for fat32 from this site:http://www.ridgecrop.demon.co.uk/index.htm?guiformat.htm

[mike rowcosm]

ok so I took out the sd card and ran the player today and the results were the same.  One thing i'm wondering is whether the battery life was affected by me selecting the 'themes' option from the menu below when I initially installed rockbox

[saratoga]

No, nothing you select in the installer will have any impact.

What was the battery life?  What is it in the sandisk firmware?

[mike rowcosm]

Thanks for replying .  Before I put rockbox on the player the battery life was around 9 hours (same time as I was getting on my other clip zip when it was new), but at that time there was about 4 gb of music on it.  Now the 8 gb player is about full, and there's around 37 gb on the card.   So I suspect this has something to do with it, along with the music file formats (most of the files are Mp3 or wma) or bitrate (mostly 320). 
In any case i'm still happy with the player even if it only lasts 6 hours (I have a nice portable charger which solves that).  I was just expecting the battery life to be significantly better with the rockbox firmware.