I want to buy a rechargeable glow plug igniter. I currently own a glow plug igniter that connects to a heavy duty battery. I'm worrying because i know with rechargeable batteries when you recharge them you have to drain the battery fully so you can keep the batteries life. So when i recharge my starter box battery I let my starter box run until the batteries are completely drained.

So when the rechargeable glow igniter can't start your car anymore how do you drain the rest of the batterie or can you just stick it in the charger with out draining the rest of the igniter???