Just to throw this in.. On my 21 horse Briggs I have lost the compression release on the cam.. When I have a battery charger on the battery or have had one on in the last 12 hours approx. or less it starts fine.. After setting with no charging for more than the 12 approx. hours there is enough battery drain off (top charge) that the engine will turn over slow and usually hang (lock up) at the decompression stroke.. It took many battery changes including known good batteries from other equipment and a couple new batteries and then an accidental reading explaining about the compression release issue. I have been running said mower for a couple years or so this way but if I try to start it after the battery has set without a charger on it for much time I have to be prepared to take my wrench and turn the crank backwards.. It will start almost every time then with same said battery.