I wrote awhile back about rechargeable 9v batteries, and why they’re an important part of my workflow, There’s a new 9v rechargeable power solution available now, the Beachtek 9v batteries. They are a hair more expensive than iPower, ($24 each in pairs for the BeachTek, $22.95 each for iPower) but they have significantly greater capacity… the iPowers are 520 mAh, but the Beacheks are 700 mAh. I recently bought eight of these batteries for my kit, since my iPowers are two years old now.
First the bad news… the new BeachTeks are just the tiniest bit thicker than iPower batteries or traditional alkalines. As a result, they WILL NOT FIT my Lectrosonics 201 receivers. They do fit in the Lectro 200-series transmitters that I have, as well as the LMA transmitters and the Lectro 211 receivers.
In the bag, this isn’t a problem… I power all my receivers with a NP1 battery using a BDS system. But if I want to use the 201 as a camera link, then I’ll need to use iPower batteries. This isn’t a deal-breaker for me, but it is something to be aware of. The BeachTek batteries will power a lectro transmitter for a full production day. so they’re great to have in my kit. But they won’t completely replace my iPower batteries.
BGilbertSound 
I have been using iPower 9v’s for around five years now. I have been very impressed with their longevity. I am tending to retire them after three years (even though they’re still decent). I usually get Production to buy six or eight new ones for me at the start of a series.
The thing I think is weak in iPower is the CHARGERS. They’re inconsistent one-to-the-other; batts that are “green” on one go “red” on another. And often if you reconnect the power supply to a charger full of “green” batts, they’ll go “red” for another hour of charging…humph.
Good to know. I only have two chargers… the latest one came in with a dead LED indicator. Sounds like the big Chinese vendor that makes these things for them has the typical quality control issues that I love to hate. On the plus side, though… at least they are 4-bangers. The Beachtek chargers can only charge two batteries at a time, which is why I bought another ipower charger instead of the Beachtek.