That solution above didn't work for me as it just changed to a different tone. This DID though....
Hi 've spent ages trying to find the answer to this, as every day the low battery noise shatters my eardrums and nearly makes me fall off my seat while wearing headphones on the train. I rooted the phone, deleted the media files, tried to find the hidden menus, froze system spps with Titanium, all for nothing. Yesterday, I got Sound Manager from the Android Market, turned System Volume to zero and hey presto, no more low battery warning! It doesn't seem to effect anything else like ringtone, email text etc either. I can't believe it was so easy! I will post this on other forums too as I would've found it very helpful. Thanks,