Holding for instructions photos
Typical Modes of failure:
Pack won't charge - Fuse is blown, physical damage, total voltage is too low for the charger to play with, or the protection chip fighting you.
Pack dies more quickly than it used to - Some capacity loss over time is normal. Sudden or dramatic loss of usage time means there is a weak cell, or one far out of balance.
Pack starts tool but shuts off almost immediately, then will start again after 10 seconds - Usually overheating, or a variation of the above with a cell with high internal resistance causing extreme voltage drop when under load.
Pack has weird flashing lights on it - Typical of Ryobi, but some other brands also do it. It is usually a code of failure, generally it means overheated or voltage too low.
Construction of Packs:
Many of the different brands have batteries that are all the same, but with a slightly different case. Some creative use of a Dremel can often allow for crossover, but be careful or unintentional incendiary experiences may result. Most packs are held together by T10 security hex screws (they have a little dot in the middle of the head). Larger yardtool packs are often T15 security. Use a good bit, clean out debris from the head with a pick. These screws strip easily. There will also usually be a sticker covering the joint of the top and bottom of the pack. If you need to use a pry tool, use a plastic trim tool or similar non-metallic option until you know the pack well so that you don't short out the innards.
Inside the packs are rows of cylindrical cells (note: DeWalt Powerstack batteries are pouch cells. Don't mess with pouch cells if you aren't advanced!). Generally for anything labeled 18-22V there are 5 cells per row, and then these rows are stacked to give you more capacity. Your job is to get all these cells to the same charge level, then figure out if there is a cell that keeps dying. These cells have a nominal voltage of 3.6V, low voltage may vary from 2.5-3V, and the top voltage is 4.2V. Never let a cell go above 4.25V!!! Cells are happiest stored at 3.7V, don't leave them on a charger, don't leave them connected to a tool, don't let them freeze, don't leave them in a hot car/laying in the sun for long.
The cells all have a positive and negative end, with the important note that the entire metal shell of the cell case is the negative! If there is a puncture in the wrapping of the cell know that metal is the negative the same as the end of the cell. The positive end will have a dip, and an insulating ring around the 3-4 "legs" that connect to the positive end of the cell. Do not stick metal pieces in here as you will cause a short very easily! Each cell (or pair of cells, if there are parallel rows making up a battery of more than 2.5Ah) will have a balancing wire going to the circuit board on the battery pack. One end of the pack will be the total positive (red wire) and one will be total negative (black, copper, or just plain wire). The pack with the purple cells is from a DeWalt, the Green are from a Ryobi. Both colors are made by LG. Don't worry about the consumer warning on the purple cells, that's from a lawsuit with some Vapers who liked to carry these loose in their pockets with their keys... The Ryobi pack I already stripped off the connections between the cells to show the positive end clearly.
Diagnosing the Issue:
First, is your charger plugged in? Is the battery firmly and correctly attached? Is there a buildup of dirt/debris, or can you see obvious damage to some part? Ok, on the outside you should see a "B+ and B-" terminal for your battery. If you can't see any markings, it's generally the 2 outermost or opposite terminals. Put in your probes, see if you get a reading. Sometimes you have to use a little piece of scrap metal to stick out if your probes are too large. Occasionally there is more than 1 terminal (Looking at you, Flexvolt). Make sure you don't short something! If you are getting a reading of between 5-15V, you probably just need to charge the battery up to 18-20V and the charger will like it. You can "jump" a low pack with a good pack to do this if you don't have a power supply. Ideally, you open the pack up however and see what the individual cells are reading.
