I buy these 2 packs of 9v batteries for wireless microphone systems and get good battery life out of them for less than a buck a battery. I buy 6 packs of 2 batteries so I have spares on hand and ready to use. For cheap. It really pains me to have to spend 4-8 bucks for a single 9v Alkaline Battery from the local store. A little advance planning saves me $60-$100 dollars vs buying last minute batteries locally.
I'd like to wait to review these after the batteries die, so I can give an estimate of how long they last. But seller is bugging me for a review now. Plus, I bought them for my smoke alarms. Given how little use the smoke alarms get, I might move before I ever have to replace these batteries! So far, so good. Work great, shipped very quickly. I'm happy I bought these.
I'm at the end of either my first or second pack of Monoprice AAA batteries and have been quite satisfied. I plan on using these 9Vs one at a time in a CO2 detector. If I have any doubts about their endurance I'll just change them more often than once a year, which would still be far more economical than using those of the leading brands. I deduct one star because they're a little big bigger than standard size and some applications for 9V batteries have them in enclosures which are very snug.