Over the last five years, I have seen around 18,000 Ultralife batteries churned through transmitters on reality location shoots.   Sitting in a 'jungle' for 21 weeks, and on islands for a further 23, gives you plenty of time to observe battery life.

 The manufacturer claims:

 "Our lithium 9-volt battery is a consumer-replaceable battery that lasts up to 5 times longer than ordinary alkaline 9V batteries and 10 times longer than carbon-zinc batteries. It has the highest energy density, flattest discharge voltage curve, longest shelf life, widest operating temperature range, and lightest weight of any comparable 9-volt battery.

A 10-year service life makes our 9-volt battery the choice for major smoke alarm manufacturers for their premium lines of 10-year ionization-type smoke alarms.

And as a consumer-replaceable battery, consumers can instantly upgrade any application requiring a 9-volt battery".

COMMENT.
I wouldn't dare question their claims, but I would draw your attention to the fact their 10-year service life claim refers only to smoke detectors which draw infinitesimally low current.

How the Ultralife performs in a wireless mike environment is interesting.

Their rating of 1200mA/Hour is achieved at the 9mA discharge rate using 5.4 volts as the end voltage.

No wireless mike TX I have every encountered drew as little as 9mA - at least any working unit ;-)

In reality, 70-80mA is more probable.

Few wireless mikes work down to 5.4 volts and most die out around 6.4 volts.  Even then, audio headroom may already be suffering.

If you increase the discharge rate to 80mA and raise the end voltage to a more realistic 6.4 volts, their mA/Hour rating dies dramatically.  You will get much less than 1200mA/Hour. In all probability, about 700mA/Hour.   Six to eight hours maximum, if you are lucky.

If you put a new Ultralife battery in a typical 100mW transmitter, it will drop below eight volts in about TEN minutes.  It will then plateau and take another 5-7 hours to ramp down below seven volts.  The drop from eight down to seven volts, is almost perfectly linear.

I did have an experience with one batch that we suspect was left sitting in the sun, on a Fiji dock, for a day or two.  These lasted between 10 and 30 MINUTES.   I hasten to add…   This can happen to any brand of batteries exposed to temperature extremes.

As we routinely change TX batteries 30 minutes before the live show, imagine the fun that was ;-) Talk about a Chinese Fire Drill!  To make it worse, nobody could remember which 'cache' the bad batteries had come from.  Don't you just love days like that?

If the Ultralife suits your needs...Buy only the U9VL or U9VL-FP versions.

The two are identical other than the U9VL-FP version comes in a Foil Packet (hence the -FP suffix).

All other versions of the battery are either clad in an aluminium housing (which increases the battery dimensions and makes them HARDER to eject) or extra long life versions for smoke detectors.

We used Ultralife to minimize battery changes and avoid contestant contact with the crew.

This they undisputedly do, but any cost/performance analysis in wireless mike applications will show little economic gain over conventional batteries. 
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