Storing a flashlight and batteries in my Red Cross DAT bag... Does anyone know if reversing the second battery in a two cell flashlight will help to maintain the charge longer?
Does the type of battery make any difference? Nicad Vs Alkaline
I know that lithium is far superior for shelf life... but what if they are stored in the flashlight?

Reversing a cell can prevent electrical contact at one end of the battery in SOME flashlight designs. This would prevent accidental drain if the switch is accidentally turned on. This can be a good way to protect the batteries.

However, if the cell makes contact and the switch is turned on, it would short out the batteries, which would not be a good thing especially with lithium batteries. It is better to install the batteries correctly, but have a method of locking out the switch.

Lithium batteries will typically have a much longer storage life in or out of a flashlight, and lower chance of leaking. Ni-Cd is not suitable for long storage because they lose a significant amount of their charge each month even if unused.

Reversing the second cell does not prevent it from getting contact in most flashlight designs. When both cells are from the same lot the electrical potential between the ends of the batteries is zero (you can verify that by putting two batteries together in the configuration they'd have in the flashlights and meassure the voltage between the free contacts). Thus there will be neither accidential drain nor shorting will occur when you leave the switch on.
This method would only be useful for flashlights with two cells. In other types the reversing of one cells may result in reversing the current in that cell which is even worse than just shorting it. So the habit of locking the switch or putting a small plastic disk on top of the last cell is safer.

I'd say choose a flashlight that won't turn on by accident. The twist bezel type is pretty safe from that.

Rechargeable batteries tend to self-discharge over a few months. Alkaline has much longer shelf life but can leak in hot weather and loses efficiency if used in cold weather. Lithium is the best choice for a standby light.

I use small plastic tabs inserted someplace in the batteries on most of my battery operated gear. My GPS, Ham Radio, camera, Miox and flashlights all have some sort of plastic tab preventing accidental discharge. The tabs either stick out of the case with the legend "remove before use" or there is a label on the case so that if someone else is trying to use the gear they will see the label and remove it. Otherwise they may think the device is broken.

I use my battery gear a lot so most have rechargable NiMh batteries. I carry enough AA and CR123 Lithium batteries to replace all the rechargables. They weigh next to nothing and insure that I will have power when needed.

I do maintain a fairly rigid maintenance schedule on the rechargables. If they are stored without use for more than a week they are recharged and they are recharged after every use. I find this is sufficient to provide reliable use with rechargables. I could not afford to buy alkaline batteries. I use the gear a lot.

The one exception is a ham radio which has a custom lithium battery. This radio is new to me (Kenwood TH-F6) and I have not gained enough experience to work out a good technique with it yet. It has the disadvantage of lower power from the alkaline AA pack. Drops from 5 watt on the lithium to 1/2 watt on the alkaline (or rechargable) pack. This makes me want to use the alkaline pack for normal use and hold the lithium in reserve, but I have no experience about how long the rechargable lithium will maintain its charge in storage. Also not sure if repeated "top off" charging without discharging is a good idea. Anyone have experience with rechargable Lithiums?

Lithiums have much lower self-discharge than ni-cads, perhaps lower than even 1% a day. And they DON'T like being deep cycled! Keeping it topped up is the best way to go with them.

Lithuims are not rechargeable, unless you are talking about Lithium Ion like in a laptop or cell phone and they are hard to find in AA or AAA size.

NiMH batteries have a worse self discharge than NiCad even. I've charged both and in a month the NiMH were too low to use and the NiCad were still useable until about 3 months. Rechargeables are great for things you use each day buy not great for storage. Lithium is the best for long term storage as they have a 10 year shelf life and they are great for BOB/PSK/Etc lits because of their lighter weight.