Mike, I know I've said this before in other threads, so forgive the repartition, but the $29 chip reader was poorly made, rushed to market prematurely, and IMO Square knows it. Have you had it for less then a year? If so it's under warranty, even if it isn't I'd write to them anyway. It couldn't hurt.
We had 4 of them. We just emailed warranty, said it won't hold a charge and they send a new one. As long as we returned the old one within 14 days the prepaid label they provided we aren't charged.
However, I finally wrote that I was extremely disappointed with this product, and I was concerned that I was being forced to accept liability for fraudulent charges because their equipment keep failing.
I said I didn't want another replacement, I asked to apply my $29 square return towards the purchase of the new (at the time) $49 contactless reader. The apologized for my problems and sent the contactless reader free of charge.
This was in October and it has never given us a single problem. It stays charged all day, it doesn't drain the phone battery either. We bought a portable charger because we had both those issues with the other Square, but haven't needed to use it.
The only downside is that the contactless reader can only pair to one device at a time. This works for us, I take payments, while Allison (she's the potter, and it's her work), wraps the purchases. This involves bubble wrap, tissue paper, gift boxes, shopping bags, etc. So, I don't have a problem keeping up with the financial transactions.
If you and Cindy both need to take payments you can still swipe sales with the mag strip reader on the other phone, I would just make sure to take large purchases on the chip reader to minimize your risk.