Variable DC Power Supply - Anyone Have One?

I keep finding myself in situations where I've got lithium battery packs (usually cordless tools) that have been overly depleted. Usually, if I can find some way of "jumping" them, I can get another couple of years out of them perfectly fine. 

Most recently, I trash picked a 80v Kobalt weed eater that was UNUSED from 2017 and the battery is dead. Or at least, the charger thinks the battery is dead. 

I'm eyeing a variable voltage benchtop power supply, something that can do 120v.

My thought is that as more and more stuff goes battery, that having some way of charging batteries manually might come in handy. My question is, what else might I use a benchtop power supply for?

Be careful with those lithium packs, the reason why the OEM charger refuses to charge them is the risk of fire.

I have a benchtop variable voltage DC supply, mainly I use it for electronics projects.  It was also useful for measuring the voltage/dwell curve on a set of coils so that I could program it into my megasquirt.

I use this one. 0-60 volts. 5 amps. It has worked successfully on everything I've needed it for, including a set of Segway batteries. 

As stated, be careful. You can explode a pack. Give the battery the minimum charge needed for the correct charger to recognize the pack. 

I don’t use one of these but have one.

I wonder if you could use a cheap model train train tansformer to tickle the battery just enough to get the factory charger to recognize it?