NiMH

Low self-discharge NiMH is miles away from the awful NiCD stuff of the 90s, and it works well enough that I only need to buy 9v batteries for the smoke detector.

What Items Do You Stock Up On? | Lifehacker Australia 2009

Li-ion is said to provide twice the energy density of NiMH, which is the battery technology used in today's hybrid vehicles.

EE Times-Asia 2008

Existing Nickel-Metal Hydride ( "NiMH") batteries power current Toyota RAV4-EV plug-in Electric cars more than 100 miles on a charge almost 7 years after the last NiMH battery they require was produced.

Resume production of EVs now that Chevron sold control of the batteries 2009

That fixes the worst characteristic of old NiMH cells.

Top 10 Battery Hacks, Tips, And Tricks | Lifehacker Australia 2009

Keeping NiMH batteries in the freezer can boost battery life by 90%.

Store Batteries In The Freezer To Retain Charge Longer | Lifehacker Australia 2010

In fact, at “room temperature” (about 70 degrees F) NiMH and NiCD batteries will self discharge a few percent PER DAY.

Store Batteries In The Freezer To Retain Charge Longer | Lifehacker Australia 2010

This is less true for alkaline batteries (freezing extends their shelf life by only about 5%) than it is for NiMH and Nicad batteries often used in electronics.

Store Batteries In The Freezer To Retain Charge Longer | Lifehacker Australia 2010

I use NiMH batteries in it and always take a spare, fully charged, set with me before I head out.

Squeeze A Few More Shots Out Of A Dying Camera Battery | Lifehacker Australia 2009

NiMH and NiCd batteries self discharge at a MUCH faster rate than alkaline batteries.

Store Batteries In The Freezer To Retain Charge Longer | Lifehacker Australia 2010

NiMH batteries stored at freezing will retain over 90% of their charge for full month.

Store Batteries In The Freezer To Retain Charge Longer | Lifehacker Australia 2010