I wouldn't be so sure about this. My new battery I received had a tighter fit than the original battery that came with it. I thought I had mine all the way in but apparently it did not click and I didn't notice. The next day I took off and got the critical battery error close by. Luckily I hadn't full throttled her yet and was just easing her out practicing recording smooth footage. I was able to get her back home safely and took her in nice and slow but I could easily see how I could have lost it in the water had I full throttled it backwards. When I checked mine after I brought it in, it had about an 1/16" gap. Sounds like when you went backwards that it slipped out far enough to cut the power if you ask me.
Pretty much exactly what happened to me. Spare battery turned up so I took her out for the first flight to start wearing her in. Was up fairly high and got the critical battery error and couldn't see how much power was in the battery. Didn't bring it back down straight away which wasn't the best choice but when I did I could see that the battery now had a slight gap between it and the housing. This new battery really needs pushing in hard and then to be sure I try pulling it out to be certain it's in there firmly. Maybe it's a new design or something.