I have a BlueAnt bt blast bluetooth speaker that I need a new charger for. It says DC 12V on the back by the power supply. I checked the manual and this speaker has a NiMH rechargeable battery. Can I use a 12v lithium charger for it? It seems really difficult to find any other kind. Also, the speaker has been sitting in storage for a couple of years and apparently you need to use NiMH batteries regularly for them to keep working. If it doesn't hold a charge, would it work if I left it plugged in? Thanks!
No, you should not use a lithium charger, or any charger for that matter.
You should use what it says on the unit, a 12V DC power supply.
The charging circuitry for the battery is inside the speaker. It knows how to charge the battery, as long as there is 12V DC supplied.