Omron BP7000 and Brother P-Touch needs lithium or alkaline batteries
Certain electronic devices can't get by with the normal NiMH batteries, for instance, our Brother P-touch PT70BM label maker needs 1.5V and it won't work with normal rechargeables so you need to install Lithium batteries if you want a rechargeable solution like these USB rechargeable AAA batteries from Pownergy or buy an ugly wall wart.
I found the same problem that is undocumented with our Omron BP7000 blood pressure monitor. it would powerup with NiMH and then just die, but using Alkaline batteries solves this as do these Lithium batteries.
The algorithm for this, is just try to put in the normal and cheap (like $1/battery) NiMH rechargeables and if they don't work, then you can for the $4/battery lithium. The payback is way longer as the typically alkaline battery costs $0.18 or so, but these batteries last 500 cycles or so, so you will catch up and save the planet too!