Poor range and randomly shutting off

A couple of years ago I installed a front, geared, hub motor and a bottle battery with a built in controller on to my commuter.

At this point the batteries are, pretty well, done for. It gets used year round, including sub-freezing temperatures. The battery is not giving more than about five miles (and in the heavy winds here, it is frequently not giving that). the other problem is that it is frequently shutting off. This is particularly noticeable on assist level 5 (of 5). If there is any sudden increase in load, such as a wind gust, the unit shuts off and I then have to recycle the power switch to restart the controller.

The battery is a bottle battery with a built in controller.

As I see it, my options are:
1. Purchase a new, similar bottle battery with built in controller.
2. Replace the cells in the bottle battery (I haven't even opened it; so I have no idea what that entails).
3. Purchase a new battery and a separate controller.

Any suggestions would be appreciated.

How much range did you get when it was new, and roughly how many miles have you put on it?

How many times has it been run way low, stored at full charge for extended time, etc?

Those are el cheapo batteries, I can share stats for a nicer one with about the same age.

Possible the battery is just worn out, possibly out of balance and needs a thorough charge and balance.

From what I have read putting new cells in one of these is a bit complicated, more so than a shark or dolphin pack, but this is way out of my skillset so not certain of that.

Likely best to get a whole new unit, you may need to consider more amp-hours for longer lifetime.

As for a seperate controller, I prefer modularity so individual components rather than entire assemblies can be replaced or upgraded more easily and at lesser cost.

I'd do 3. It might be possible to dissect out the controller, and still use that.

Yep. Obviously, you need better power and capacity. Buy a bigger battery. Saving the controller is possible, but cheap to replace with one that will have its own enclosure, and set to match your new battery capabilities.