Resuscitating 'dead' lithium batteries

A mate dropped past and was having a whinge about the cost of replacing some 'dead' lithium batteries that were so low in voltage they wouldn't even start charging. He was particularly frustrated after buying a series of very expensive chargers that perfomed exactly the same as his older ones.
Connect the battery, throw the switch and the charger would simply throw up an error showing the batttery was toast and refuse to charge it.
Eldest brother, who's a mechanic in a past life, quietly asked him to grab them out of his truck. Ol' mate grabbed one, connected it up, threw the switch and triumphantly showed the charger saying, sure enough, it was as dead as a dodo.
Brother says nothing, wandered off before coming back with a spare good battery which he connected to the dead battery. Plugged in the charger and voila, the 'dead' battery starts charging! After an overnight charge he took the dead battery, threw it in the truck (running a fridge) and it's been running fine for the last few weeks.
The trick is the second 'good' battery tricks the charger into believing the voltage is high enough to start charging. What was even cooler is they weren't even the same voltage, the good battery was 18V and brought to life a 12V battery. (Edit: the good battery cannot be a lower voltage than the dead battery, ie: dont try and use a 6V to start a 12V. Same/same works fine, ie 12V v 12V.)

Two other mechanic mates regaled with story nodded in agreement, turns out it's a trick they've all been using for years.

So before you toss those annoying expensive flat lithium batteries you've had kicking around for ages from that drill, caravan or whatever, give this a try. You might be pleasantly surprised.
Cheers!
SB

I have found the same thing , smart chargers are to smart sometimes, i revert to an old transformer charger to start the charge for an hour or so , then back to the smart charger, on lithium battery i use a 12 volt power supply

I've been selling lithium powered skateboards for more than 10 years. jump starting the charging process can be done by raising the "dead" battery's voltage by connecting to a same but charged battery in parallel. the BmS wil not allow charging if the minimum voltage is lower than a preset minimum voltage. The hood battery averages the overall voltage to above minimum safe voltage level and the BMS will begin charging. Some cells may be damaged as a result of the over discharge and cannot be revived, this reduces the overall capacity of the pack. They can be individually replaced but putting new cells into an older pack is not ideal and can be expensive to do. we deal with loads of lithium battery issues whether it be BMS, the battery or the controller. I still wouldn't have lithium battery's on an offshore boat. The tech is still too primitive and will be replaced before too long with a more stable, better capacity alternative. great for camping and power tools, imho, not for boats.
DM