Aha! One of your Atlas 40V batteries doesn’t want to charge. Plug it into the charger and nothing happen. You’ve cleaned its contacts and yet it still won’t work.
It’s not a dead cell or a busted charger. Nope, it’s sleeping. Its internal protection circuit turn off when the battery reaches low voltage. That turns off the charger so it won’t see the battery. Connect it to another battery (a donor pack) to bring it back to life.
Jump Starting a Dormant Battery
This means you take just enough charge from other battery to trip the dormant battery‘s detection circuit. For this you will need a functioning Atlas 40V battery or something different than same voltage rating like a 36V-40V pack.
To connect them, you first lay them side by side on your work area. Before hooking up, you want to know which terminal is which. Hooking it up incorrectly can be very damaging. Using a digital multimeter, locate the positive terminal on both packs. On single cell, you should read approximately 3.8 volts. This help properly map out how everything connects.
Here is another data point. Check the overall voltage. A quick look at the multimeter shows almost 40 volts between main terminals. This verifies that battery structure is intact from an electrical perspective but requires a jumpstart to come alive.
Precision matters. No guessing as to which wire goes where. Use red and black wires to connect the bridging leads. Make sure positive connects to positive and negative to negative. Twist them securely around each of the contact points on both batteries.
After you leave them connected for maybe 15 seconds, there is time for enough current to cross over, even if only slightly. Although it won’t be noticeable by looking at the dormant battery, the batterys voltage will increase inside. That’s what breaks the low-voltage lockout state and makes the controller recognize again that pack is present.
Unplug the wires and plug the revived battery into the charger. Now the charger sees the pack and feeds it electricity as usual with no issues, and the indicator light turns on right away.
The reason this works is because most chargers require a minimum voltage threshold for communication. The battery drops below the point where it’s talking. Then when you raise the voltage slightly over that point, the charger regain contact.
This is basically the same principle behind several other reset battery techniques and saves one more pack which would of been thrown away if not.
