Correlation between Hybrid battery issue & gas gauge dropping?

I posted a month or so back about the hybrid battery issue on my 2008 prius. It seems it can be fixed with a new ecu and wire harness. Unfortunately, I can't find any mechanic who can do this so I may go with an inexpensive battery switch and trade it in for a new car. I hate giving up my battery though for one that is used and may be weaker. I guess it's a gamble. However, my new question is about the gas gauge. I had 3 pings on my gas gauge when I parked the other day at my house. Yesterday, I drove a half mile to the post office, saw the 3 pings on the gas gauge, and said to myself I should fill it up to at least half. Then, when sitting at a red light all of a sudden there was one flashing ping! Thank goodness I notice it, and of course I hit every red light on the way to the gas station! I filled up the car and the gas gauge indicated one less ping that full. What would have caused this sudden drop & would it be hybrid battery related? I've never had this happen on this car and I bought it new in 2008. It's been such a great car, I hate the thought of giving it up. Thanks in advance for any advice.