For about a year now my 2015 Mazda6GT has been giving me the dreaded "check battery" type alarm. Basically saying my I-Eloop battery was shot. Looked at many forums and seemed like everyone was saying you had to get the Mazda one from the dealer, but at almost $500 there was no way I was going to do that. So I ended up going to NAPA and getting one of their AGM Batteries. About $175. Put it in and drove for around 10 miles just to charge it up completely and what do ya know, works fantastic ! No alarms, my I-ELoops regenerative screen on the dash works the same as it always has.

So in other words don't go buy a Mazda I-Eloop battery for $500.

 

All you needed was a replacement Q85 battery, lots of battery brands have a Q85 in their range.