I bought a SH Dewalt 24V DC224 off eBay for £100 a few years ago. Drill last OK but later batteries down to about 4 holes drilling for 10mm through bolts in rock.
Shopped for new battery on ebay again found one with larger capacity than manufacturers original and Sanyo batteries in it. (Sanyo is a buzz word to me) for £60
Drill about 8 to 10 holes, no need carry spare!
Not as good as Sinkers kit but fair for what I paid for it and the drill is lasting well.
Rock can vary, slate and mudstone gets eaten, probably do a lot more holes, but vein rock can be quite hard and you start to wonder whats happening.
My avatar is a poor likeness.