These controllers can have problems charging batteries and that is easily mistaken for a bad battery. It may claim a battery is fully charged when it is not. There may be other problems. I haven't seen many deflective units so I don't have a lot of information on the problem but there is a voltage regulation circuit that handles both converting the voltage to the 3.3v required for the unit to operate and also controls charging the battery. This regulator chip has been known to break. It may short out the battery causing the internal circuit protection to shut it down. It could drain a battery more quickly. It could not fully charge a battery while the LCD display claims otherwise.
If you replace the battery and it only lasts one charge, then won't re-charge that is very likely to be a problem with the controller and not the battery.
I have an external Lithium battery charger and a load tester. I don't test every battery because this takes 3-4 hours, but I have enough experience to know that it is extremely rare for new batteries to have trouble charging, holding a charge or not lasting as long. Usually when I see a new defective battery, it's dead because once one of these drops below ~2v it will never work again. So if there is a problem in manufacturing then the battery is usually dead before I come across it. Unlike NiCd and NiMH batteries, Lithium cannot be recharged when the voltage drops below a certain threshold. The exception is that these batteries also have a protection circuit which can turn off the battery to protect it, so it can measure 0v at the wire leads but still be recharged because the cell itself is not 0v.
Here is a photo showing a damaged power regulator IC. You cannot always visually see a problem. The IC can be severely damaged without any burn marks.
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Customer reporting a problem that a new battery fixed: All the LEDs would come on with no display when plugged into power. Unplug and it would stay like that for 10 minutes. Then the display would read no plow.
