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Installed overhaul kit for flotec pump that includes new impeller, o-ring, gasket etc.
What’s inside a lithium polymer battery pack? Not much. In this case, six pouch cells with 5.8Ah (amp-hours) nominal capacity, nominal voltage is 3.7V (volts) per cell, making this a 22.2V battery pack since all cells are connected in series.
The “C” rating shown on the pack is a claim by the manufacturer, telling the maximum operating current that can (supposedly) be drawn from this battery. Manufacturers often additionally claim even higher numbers for short periods of time, calling that the “burst” current. The “30 C” rating stated on this pack allows for up to 174A to be drawn without damaging the pack (30 times nominal capacity), but no claim for a “burst” current is made.
In reality, many packs do not live up to their specs but the user never notices since only very short peak currents are drawn. When stressed to the limits or beyond, the tabs on these batteries burn off, de-facto acting as a fuse. When burning through tabs, batteries can catch fire. There are many videos on Youtube showing lipo fires, some of which are very vicious.
Use extreme caution when working with lipo batteries. Store them in a place that would allow them to burn without setting your house on fire. Lipo batteries (many different brands) have been known to catch fire a day after having fallen to the ground, not having shown damage.
Never charge without supervision. Use only appropriate chargers. Never over-charge. Never over-discharge.
The battery shown in this video was used by me from 3.5V per cell (which I consider as empty) to 4.2V (full). Many users allow for more discharge, down to 2.8V to get a bit more capacity from their batteries, but the deeper the discharge, the shorter is the battery’s life time. I have had lipo batteries that I never discharged below 3.5 V and never charged to more than 4.1V and reached more than 1000 charge-discharge cycles with almost no noticable capacity degradation.
Armed forces using lipo batteries spec these for use with less than the nameplate rated maximum voltage for exactly the same reason: They want these batteries to last for thousands of charge/discharge cycles. Using a 4.22V (max) rated lipo to a max charge voltage of only 4.1V does achieve a noticeable lifetime improvement. But it comes at the expense of having just 80 to 90% of the nominal capacity available. Given how vastly better lipo batteries are (weight, power, energy) compared to older technologies, that is an acceptable drawback.
The dissected pack in the video had one bad cell that always dropped to my low-volt threshold way earlier than the other cells in the pack. The most reliable way I found to identify bad cells in these packs is to charge the pack (to 4V or 4.1V per cell) and let it sit for a long time. Good cells (in good quality batteries at least) show extremely little drop in voltage, bad ones can lose 0.1V or even 0.2V per week. There is no way to fix them that I know of.
My attempt to take out the bad cell ended in the destruction of most of the other cells. I’m sure there are people out there who know how to do a better job than I did. My money is on dental floss to separate pouches without damaging them. I’m sure I’ll find it on Youtube, if not now then maybe soon.
[Edit 2016] – *Best solvent to separate cells* is white gas, a.k.a. camp stove fuel, a.k.a. white gas or naphtha. It doesn’t stink too much, and I always have some ready with my camping gear. WD40 works too, but is smeary. And I’m sure there are others that work just fine.