DJ, if you start to use a battery charger for this... ( and I don't know if that is a good idea ) ... keep in mind that some of them require a voltage sensed from the item ( battery ) before they will output electricity... ( ie, when I have a really drained farm battery I have to jump wires from a good battery before it will activate the charging circuit.... once it gets ' some' juice ... then the other battery can be taken out of the loop...
Did not want you to think a plug was bad because it did not heat up with just the charger ( if you have this type )....