There is no way that I know of to disable the low battery alert. Beyond that, if you are using Express mode make sure to set the exposure to auto. If you are using Classic. Make sure you are only saving photos or a video but not both and don't do any processing of any kind.
Finally make sure everything else is turned off. Put the phone in airplane mode and kill any apps that may be running in the background (Skype, music apps, disable automatic email fetch, etc.). Do not disturb may also be useful but I'm not sure.