I work on Boeing 737's the baggage area is pressurized. As far as I know this is the case for all pressurized aircraft. It would be very difficult to make them with an unpressurized baggage compartment. It may not be heated though as is sometimes the case.
Tom
Thanks for the info, I have had bottles of bath items empty in checked baggage from air pressure issues.
Here is info on batteries..
Airline restrictions on Li-ion Battery transport
Rules clarified on flying with lithium batteries
Posted 1/11/2008 12:34 AM | Comment | Recommend E-mail | Print | Reprints & Permissions | Subscribe to stories like this
By Jayne Clark, USA TODAY
The Department of Transportation has reissued its message — which apparently got lost in translation the first time around — regarding new restrictions on how batteries can be carried on airliners.
As of Jan. 1, travelers can no longer pack loose batteries (i.e. those not installed in electronic devices) in checked bags. However, unlimited loose batteries are allowed in carry-on bags, though the agency "strongly recommends" separating them in individual zippered bags or compartments if they aren't in their original packaging.
One exception: Passengers toting lithium batteries that have 8 to 25 grams of equivalent lithium content are limited to two uninstalled batteries in each carry-on. Most consumer electronic goods such as laptops, digital cameras and cellphones use batteries that fall far short of that content. The rule was implemented to reduce the risk of lithium battery fires.
http://www.bobatkins.com/photography/li_battery_restrictions.html