After around 100 flights across 4 batteries.. I took my bird up when the battery was around 55% for a planned short (few minute) flight over a cliff face. Just as i got off the ground and about 10-15 meters out over the cliff the battery alert on the Mobile app came on and the battery showed around 5% charge left. I was quite scared and wasn't sure if the bird was going to drop out of the sky (over a very steep cliff) or not. I hastily brought it back home. What i noticed was the bird was loosing about .5m/second in altitude on it's own (with sticks centered) and second if i did increase the thrust it was only gaining about .5m/second in height. It was quite disconcerting and i was unable to take time to find a good landing spot. It landed on a rock which was slightly angled and although landed okay, it keeled over as the propellers were slowing down and scratched the body of the drone and the two props at the front (camera side). After changing both props and battery I then tried for another flight. Just as it was about to lift off, one of the (changed) propellers flew off (literally) into the air about 4-5 meters above the drone and over the cliff face. At the same time the drone tipped over (in the direction of the prop that came off) and the other prop next to it on the rear (battery facing) side shattered as the drone keeled over. The propeller that flew off was on the opposite side (undamaged/unscratched) to where the drone had hit the ground before. Now, I have scratched on front and back of the drone casing.I'm also alarmed the prop would fly off like that which i suspect meant the motor or some connecting component failed. (lucky it happened on the ground) What should i be checking at this stage? How to test in this situation before flying at height? Those batteries have had about 25-40 recharges and full discharge around every 20 charges (I keep a log). I noticed a few of the batteries are bulging slightly which i have heard is a sign to stop using them. I wouldn't mind if it was just one but all of them look like they are bulging a bit. Is it possible to change just the cells inside the batteries?