Yeti 400 overheating

We have had ours for 4 years and really only use it when we camp for coachella. We have always had a problem with it getting to hot and have to turn it off but now it overheated first day and lost all its charge from only charging 2 phones. We tried to put in on solar panel to charge but it will not charge at all. My brother has older model yeti 400 just not lithium battery and it works amazing, that’s what sold us on the product . Anyways Your feedback/help would be greatly appreciated! Have a good day and thank you in advance

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