I was in an auto parts store and they had trickle chargers for car batteries on sale for $8. The charger is just a brick with leads and clips that puts out 13.5v @3A.
So I bought one and jury rigged it to my MP890 power plug and plugged it into my 890 hoping for the best.
Nothing bad happened
No magic smoke escaped. The charge light on the MP went on. The MP powered up OK. Everything seems OK.
The point of this story is you don't have to spend 20-30 bux for a MP800 charger if you scrounge around a bit at an auto parts / electrical parts store.