Can I use LP601730 3.7 W 250 mAh to power my MKR1010 ?
Note that 3.7V batteries can reach more than 4.2V
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The microcontroller on the MKR WIFI 1010 runs at 3.3V, which means that you must never apply more than 3.3V to its Digital and Analog pins. Care must be taken when connecting sensors and actuators to assure that this limit of 3.3V is never exceeded. Connecting higher voltage signals, like the 5V commonly used with the other Arduino boards, will damage the MKR WIFI 1010.
Li-Po battery minimum capacity is 700 mAh. Smaller cells will be damaged by this current and may overheat. It is strongly recommended that you select a Li-Po battery of at least 700mAh capacity. A bigger cell will take more time to charge, but won’t be harmed or overheated. The charging circuit is programmed with 4 hours of charging time with a max of 1400 mAh per charging round.
Source: Using the Arduino MKR1000 with ThingSpeak – About Things | A Hans Scharler Blog