Charging external battery via cig lighter

[seagull369]

I like to keep an extra 12V battery in the back my truck, just in case I need to give myself a jump. Instead of dragging out the household charger to keep it topped off now and again, I was wondering if I could just charge it via the cigarette lighter using a cig lighter plug and alligator clips. I wouldn't plan on using the plug to charge the battery if it was in a near or fully discharged state. The run would only be about 3 feet.Not sure if this is the best idea, so thought I'd run it past you guys 1st. I believe the lighter circuit is fused at 15A,

Any thoughts?

 

[Zewnten]

Cigarette lighter plugs usually don't have very large wires supplying power, another issue would be float charging the battery .I'd recommend picking up a lithium ion jump pack.