With all the advance mentions of how quickly the DP2M/DP1M rips through batteries I did a little experiment and may have come up with a possible solution.
When I ordered my DP2M from Sigma I also ordered their SAC-5 accessory that provides the camera with power in indoor (or power accessible) situations. Basically it consists of a power supply you plug into an AC outlet and a 'dummy' battery that fits in the battery compartment. The dummy battery has a cable that fits through an opening that's normally covered with a rubber gasket that covers the opening.
The end of the cable fits into a matching power connector at the end of the cable coming from the power supply.
I made two voltage measurements. The first was to measure the typical voltage the rechargeable batteries put out. The other was to measure the power coming out of the SAC-5. Interestingly enough the rechargeable batteries produced about 3.4-3.8v. But the SAC 5 unit produced 4.4-4.9v. Obviously Sigma felt the camera could handle that voltage.
The Sigma batteries have a rating of 1250 mAh (milliamp hours). Clearly what's needed for longer term usage is something that can put out a much higher amount.
I then went to RadioShack and found they had 1.2v NiMH Batteries rated at 5000 mAh. Which to me meant they had the potential of lasting 4 times as long as the battery that came with the camera.
I then purchased the following.
3 x "D" size NiMH batteries rated at 5000 mAh to provide 3.6v @ 5000 mAh (2 packages of 2 D Cells @ $14.99/package)
1 x 3 Bay Battery Holder ($2.79)
1 x Replacement Adaptaplug (Radioshack code 273-350) which is used to attach two wire leads to an adapter that fits any number of power plugs ($4.99)
1 x Adaptaplug "H" tip (to fit the cable lead from the Dummy battery) $6.99 (Note the tip has an orange 'O' ring)
I then soldered the leads of the adapter to the leads from the battery holder and wrapped them with electrical tape. NOTE: The red lead should be soldered to the wire with writing on it. That's the wire that connects to the (+) center of the Adaptaplug. This will insure that polarity is correct. But to be sure I tested it with an inexpensive Digital Volt Meter
When the whole thing was completed I now had a battery pack that provides power for really long periods of time.
The 3 rechargeable D cells SHOULD output 3.6v but I've measured it at 4.6v which is still within the voltage I measured off the dummy battery connected to the AC power supply.
I've attached photos to show you how the whole thing looks.
Note: you can see the dummy battery also clears John Milich' superb grip that he fashioned for the DP2M/DP1M
Last comment: RadioShack also has a superb charger that can handle 5000 mAh batteries including AAA, AA, C and 9v as well. It also has a car adapter for use on the road as well as a USB port for charging USB devices (like phones). When charging, individual lights for each battery in the one of four bays light either red (charging), green (charged) or blinking (defective/unchargeable).