2005 chevy blazer battery drain issue
 

hello everyone i,m new here and a have a question about my blazer.my battery was draining down to about 10 volts after 4-5 days and when i went to start it it would click due to the battery being low.it would boost fine and fire up easily.now just recently after i got it boosted and let it run for 10 minutes i noticed that after i shut my engine off and remove the key from the key tumbler.i would say within 2-3 minutes the temp gauge and fuel gauge would come up to half and remain there with the key out and engine off.
so i,m thinking this is my issue and was wondering if anyone has come across this issue.now before i bought it from a buddy of mine he had a after market fuel pump assembly put in and the fuel gauges works eractic off and on.also when i disconnect the battery the two gauges will remain in the half positions until i reconnect the battery and start it.i have tried starting it and shutting it down and the same thing happens every time.any help or suggestions relating to this problem is appreciated.