Hello Jonay,
We are glad you like the construction of the slipper and the fit. That is a very important aspect of this product as well as the actual heat they provide compared to lesser products. We understand the disappointment of not having a gauge on the battery. We could have put a gauge on the battery or used one of our other existing batteries that have this function. That would then change the size or output of the battery. The reason we chose to use the new VPS826HV battery for the slippers is that it is super slim, lightweight and packs a huge punch. This equals longer runtimes and higher temps.
Two years ago we did a survey with hundreds of existing customers. These customers dated all the way back to 2010 when we launched the first generation of this slipper. One of the questions centered around which attributes are most important when considering heated slippers. Heat output was #1 and heat duration was #3. #2 was fit/comfort. Not one customer listed a need to 'tell how much battery life is left' on all of our survey’s that were returned.
We appreciate your business and hope that this helps you understand why the product is designed the way it is. Stay Warm!!!