DOOGEE claims that its latest rugged phone, the S59 Pro, has a battery capacity of no less than 10,050mAh. This power-pack apparently allows it to last for 18 hours' worth of gaming or video playback, 50 hours of audio playback or up to 768 hours on standby. Then again, with a MediaTek Helio P22 SoC, it could indeed last this long.
https://www.notebookcheck.net/DOOGEE-announces-the-10-000mAh-plus-S59-Pro-smartphone.508194.0.html