How to prevent the battery capacity degrading using a PowerBook G4 with Ubuntu 16.04?

I have a 2005 PowerBook G4 which I dual-boot Mac OSX 10.5.8 and Ubuntu 16.04 XFCE. The 'book runs both OSs quite well but I have noticed that using Ubuntu has the effect of reducing the battery capacity quite qucikly. For instance today, my aftermarket battery was showing "full" at 64% but after using Ubuntu for 45 minutes it went to 0% and shut down. When I recharged it, it only went back up to 35%. This has happened before and I am writing this post from OSX while I re-calibrate the battery. Is there any way to use Ubuntu but be gentler on the battery? I normally use Ubuntu more than OSX as it is still getting security updates and I like some of the applications that run on it. Update: The re-calibration seems to be stuck at 37% so not going very well.