> Like what caused both to go bad?
Check the blades and see if they hit a stump, rock, or curb. If a running electric motor suddenly has it's rotor stopped, it sends a huge spike (draw) and if that is not accounted for it can fry the controller or motor and/or the batteries. Usually it just takes out the controller (blows a fuse if lucky enough to have one) and the battery is fine.
Check the tires. Maybe they were spinning on wet grass at full throttle and then hit pavement such as grippy blacktop.
google: "what happens when an electric dc motor suddenly stops spinning"
a: "When you stall a dc motor you get stall current and this is usually several times full rated load current. Because the motor is no longer spinning, the natural back-emf isn't present and the full 9 volts is applied across the armature coil resistance."
The Direct Current Motor
farside.ph.utexas.edu
"For this reason, the power to an electric motor should always be shut off immediately if the motor jams"
from the repair manual you posted
> If the voltage is less than 21v, replace the battery.
This tells me the pack should never be under 21v, it will not charge until the packs are 21+ and you must have a break between cells. Because a LI battery should still be 18v just sitting around a year later if the charger failed, and should not self discharge down to 12 or 3 v in a short amount of time from 21v.
If you can find evidence that one of the motors had a full stall, the batteries are going to be junk, UNLESS such high drain melted a tab within the battery pack and saved all the batteries behind it. I suppose a bad zener diode could allow the batteries to drain if the packs were still installed in the mower.
If you find a way to measure the voltage far back from the connector, you will probably find individual cells still at 3-4.4V (just a guess looking at what CC might be using for cells) or the series behind the break might be at 36+V. In that case you only have to replace a few cells.
> shorted from the naked eye
Can't tell with the naked eye. The days of fixing a computer at board level with a DMM, simple scope, and logic probe are in the far past. Even the A/C frequency is so high now on most cable systems (coaxial) such as Comcast you can not even measure it with a normal DMM.
fwiw: When I said "AC voltage" I meant it appears that A/C is applied directly to the battery pack, I would assume to condition the pack or to run the BMS while charging. I don't know why, I am not an EE and I do not play one on TV.
If you watch enough " i converted my LT/GT to electric" videos some of the things people learn are DC motors use a PWM board and suddenly stalling their 1800 watt or 36v DC motor results in losing their whole project including the board. There are hackaday articles on how to prevent the damage if you are interested.
If you measure a cell farthest away from the connector and it measures < .5 you can assume the whole pack is junk. If the control boards on the pack are not available, you really do not want to replace all the cells only to find out the board is bad. Buy your (Panasonic) cells from a quality supplier such as Jameco or Black Box, not Amazon or Flea-Bay. $0.02
$100 for that mower is a GREAT deal. You can get double that just for one of the drive motors, I assume it has two.
1side battery pack reads almost 12v and the other reads almost 3v theyre 56v 30Amp battery packs
