My nephew next door recently purchased an almost new Inspire 2 with 4 batts, the 4 series camera, charger hub and case from a pawn shop for only 1500 bucks.

The drone and everything appear totally new....So yesterday he charged all the batteries and the controller and installed Assistant 2 and updated everything including two of the batteries installed in the drone, which two batteries we non't know...He then removed the batteries and returned it to the case.

So ok, then later yesterday evening while he is learning about the drone, he discovers it is showing a Battery cell error on his mini 4 screen.....So we swapped just one battery at a time until the error disappeared, then identified which battery had the bad cell....He could not answer which batteries were in the drone when he earlier that day performed the update....MAYBE that is the problem?

So I came home and spent several hours reading up on the Inspire 2, and all about bad batteries and I'm thinking he needs to reupdate with that battery installed....MAYBE?

It was while I was there and after examining all the batteries I discovered two of them had stickers on them that served to disignate they were paired, and I showed him web pages that described how he must always keep them paired in use and swap the pairs as pairs and always recharge them as pairs....But he could not tell me which batteries were in the drone when he performed the update....hmmmm

Do you folks here know of a link that can show him how to check each battery?

Thanks in advance!...I'm a drone newby struggling with my first drone, a Mavic Pro, so not much help to him.
Keith

You are correct that the batteries should be kept and used in pairs.

Suggestion 1: Put paired batteries in drone, turn on everything and wait for few minutes. If batteries have old / inconsistent firmware you will get a warning in DJI Go.

Suggestion 2: Charge up all batteries, let them sit for at least 72 hours and re-check. Supposedly the batteries will rebalance the cells within those 72 hours.

Always use them in pair,  update is detected automatically, when it shows inconsistent firmware it will prompt the update process... many reports seen lately about batteries issues, how many cycles the batteries have  will affect its functionality, when differences are shown between cells, full charge and let them rest for 72 hrs it’s recommended..., if it keeps happening I recommend you to get a new pair, 1500 its more than half price.... a little investment will assure the purchase....