I recently got one of these TalentCell lithium battery packs to provide backup power for my 536 in the event of the loss of AC power:
https://www.amazon.com/gp/product/B016BJCRUO/
It uses the same size 12V power jack as the 536, and comes with a Y cable so it and the 536 can be connected in parallel. The charger outputs 12.6V @1.5A, and doesn't seem to create any interference when powering the 536 and charging the battery pack. You can't use the DC power adapter that comes with the 536, because it doesn't output enough current to charge the battery pack, and its voltage is too high (14V vs 12.6V) and would probably fry the battery pack if it wasn't damaged from excessive current draw while the battery was charging.
The battery voltage swings from 12.6V fully charged to 9.0V fully discharged. I've been running my 536 off this pack with the Uniden GPS puck and Wi-Fi connected and powered by the scanner, volume level 15, and display backlight off, and it's been running for 24 hours so far and the battery voltage is still 10.65V. Since pretty much all of the 536 internals run off regulated voltages (3.3V, 5V, 8V, etc), I haven't observed any issues with running it off slightly-below-nominal DC power. So far it appears that 24 hours off a full charge is doable even under worst-case conditions (max volume, max backlight, heavy traffic, etc), and under normal operating conditions, 48 hours is pretty doable.
The photos below show it in operation.
https://www.amazon.com/gp/product/B016BJCRUO/
It uses the same size 12V power jack as the 536, and comes with a Y cable so it and the 536 can be connected in parallel. The charger outputs 12.6V @1.5A, and doesn't seem to create any interference when powering the 536 and charging the battery pack. You can't use the DC power adapter that comes with the 536, because it doesn't output enough current to charge the battery pack, and its voltage is too high (14V vs 12.6V) and would probably fry the battery pack if it wasn't damaged from excessive current draw while the battery was charging.
The battery voltage swings from 12.6V fully charged to 9.0V fully discharged. I've been running my 536 off this pack with the Uniden GPS puck and Wi-Fi connected and powered by the scanner, volume level 15, and display backlight off, and it's been running for 24 hours so far and the battery voltage is still 10.65V. Since pretty much all of the 536 internals run off regulated voltages (3.3V, 5V, 8V, etc), I haven't observed any issues with running it off slightly-below-nominal DC power. So far it appears that 24 hours off a full charge is doable even under worst-case conditions (max volume, max backlight, heavy traffic, etc), and under normal operating conditions, 48 hours is pretty doable.
The photos below show it in operation.