An unreasonably high reading like that is a common symptom of a weak battery in a cheap meter. The right solution is to replace the battery.
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Ohhh okay i'll buy a new 9V for it then i'll test it again.
Or should i wait until it just dies with that battery?
I'd test it with a brand new battery right away, and see if that changes anything. If so, then the old battery is too far gone to use reliably. Any sort of "calibration" you do would be useless, because the old battery is steadily changing its voltage, and a meter with a changing voltage reference will give inconsistent readings that vary as its voltage reference changes.
On the other hand, if the meter behaves the same when using a new, fresh battery, then maybe it is consistent, but wildly out of calibration.
Another reason to try a fresh battery right away is to see if the display is any different. I know that, on one cheap meter I tested, its LCD displayed a box that vaguely resembled an automotive battery when the battery voltage was too low to use the meter properly. But unless you knew that this was the low battery indicator (and there was no mention of it in the instruction manual), you could continue to use the meter for a long time while the displayed voltage would get further and further away from the actual voltage.
If you can get an old working Fluke 10 for a good price, I'd probably buy it and use it directly, instead of using it to calibrate an inconsistent meter. Every Fluke I've looked at has the right circuitry so that, as its battery dies, the meter stops displaying readings and shows you a "low battery" indication of some sort. You can't get it to display an inaccurate reading due to a low battery.