They look like they could do with a good feed. Bananas like a rich soil and plenty of water. I stop feeding and watering mine at this time of year, as it will shortly be going in the greenhouse for the winter, and as frosts start, I cut off all the leaves and wrap the stem in fleece. Banana leaves tend to split if they are in a windy place. If you go to a windy caribbean island, all the banana leaves look very tatty, and the bunches of bananas are protected in large bags. If the stem does get frosted, chances are if the root ball has been kept on the dry side and not frozen solid, new shoots will come up from the base to replace the original stem. Bananas are botanically a herbaceous plant and not a tree.
This is my banana basjoo. Bought for £5 earlier this year and about quarter of the size it is now. I've brought it into the summer house where it'll get any afternoon sun, heating maybe at weekends. What else shall I do with it? Water or not? Leaves on or off? Wrapping? It's still growing happily at the moment.
They do tend to behave this way, also in the wild. Like many plants they drop leaves that do not get sun, also like figetbones said, feeding could help. Here is how they behave in the wild:
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