Magic Mouse battery levels problem

[chichots]

I have a 2009 MacBook Pro and use older version of Magic Mouse. Now, the trick is that this computer very quickly pops up a notification of depleted battery, but when you restart computer the battery level rise up. If you use it with different computer battery lever is much higher and doesn’t deplete so quickly.
Example:
I put new batteries, 100%. After 1 or 2 hours the mouse lags and the notification pops up that the battery levels dropped to 3%. I restart computer and the levels rise to 40%. If I connect the mouse to different computer it shows battery levels are even higher but still quite low for only 1h usage: about 60%.
I have El Capitan system.
Why. Is it a system problem? What should I do?
I would sincerely appreciate the help.

 

[IWT]

A warm welcome to Mac-Forums.

Until more intelligent options are suggested by my colleagues, the two things I'd do are:

1. Reset your SMC - https://support.apple.com/en-gb/HT201295

2. Reset your NVRAM - https://support.apple.com/en-gb/HT204063 and http://thenextweb.com/lifehacks/2010/12/04/how-when-why-to-reset-the-pram-smc-on-your-mac/

Ian