Hi this is pretty straight forward.
You can use any UPS that is rated at 210watt or higher. These chairs don't draw much and they never exceed that rating unless there is a serious short circuit that could happen in the electronics but even that would likely just blow a fuse in the UPS.
So really, any one above the 210 watt will work fine for this application. If you have one in mind let me know and I can check on tat if you are still unsure;-)
In any case, I will stick with you until this is complete.
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