I think MaxxAmps has a low voltage dector that has a little LED that lights up when the pack voltage gets low. Just mount the LED on the panel by the switch for the box. When you turn on the box if the LED lights up you know it's time to recharge the box.
You have to buy the one for the # of cells you have in your pack, it looks for a specific voltage. So basicly don't buy the one for 3 cells if you have a 4 cell pack, you will over discharge your pack.
I just went and checked, they do still have them. And I was wrong, the LED is lit while the pack voltage is still good and goes out when it's time to recharge. NOTE, these are NOT cutoffs, just voltage detectors to let you know when to recharge your pack. Light goes out at 3V/cell. The safe voltage you DON'T want to go below is 2.7V/cell. They have a small cussion built in.
Low voltage dector
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