I have a handful of the current generation Milwaukee batteries. Lately, a few have whacked out on me. My larger M18 8.0 battery when charged will show 2 bars but die in about 2 minutes when being used. Another will charge fully and after a bit of use, the battery indicator will start flashing...
****UPDATE*****
So I did a little amazon searching and came up with a pump that I think will fit. A few more measurements will confirm it.
YAMATIC Max 3000 PSI Pressure Washer Pump
My new concern is whether or not the stock 3.75hp motor can work a pump rated for "Vertical engine at 6.5 ~ 7hp...