s_mack wrote:...From ...another thread on this forum..., I went through ... diagnostics... . I expected it to fail one or more of the voltage/current/trickle tests but it passed everything. ...
We have learned quite a lot since the time of that old thread, but we will never know everything we'd like to about the charging-control process. I would suggest repeating Tests-15 & -16, but don't depend on the routine to tell you about pass or fail, use your hand on the battery, this way:
1) Step into Test-15 (BTW, did you notice you can reach the higher numbered tests by reverse traveling via the SPOT button?!), and after plugging in the PSU's dc-cable let Roomba remain in -15 for about half an hour. Put your hand on the battery at that time to determine if it feels warmer than it was when you started Test-15. If warmer, the implication is both charging FETs are passing current before they have been commanded ON -- if so, they are kaput, or their driver xstrs are stuck ON (not likely, but would require lab testing to find out). Probably, the battery will still be at room temperature.
2) Next, step to Test-16. Roomba will command high-rate charging to begin. Again, you will have to wait for time to pass before the cells heat, and that heat flows to the battery-case wall, so, give it at least another half hour, followed by feeling the battery case for warmth. If the case is as cool as when you started, one or both MOSFETs have not switched closed, hence no charging current. If so, one or both FETs are kaput, or one or both of their driver xstrs are stuck OFF (not likely, but would require lab testing to find out).
Disconnect the PSU, and pull the battery to end testing.
Of course those tests depend on the PSU working properly. To confirm that a no-current result from Test-16 actually means failed FETs, you must load-test the PSU using some dc-resistance that will draw one ampere, or a little more, from the PSU.