Hi there,
I bought an Arduino model MKR1010 for my project and a Li-Po battery with JST, 3.7V 1200mAh rechargeable, but the battery connector wasn't compatible with the Arduino. Could someone tell me which is the right battery plug type for the JST connector of Arduino mkr1010?
Thanks in advance!
From the site under FAQ:
https://store.arduino.cc/usa/mkr-wifi-1010
look for PH2
Battery connector: The connector is of type JST S2B-PH-SM4-TB(LF)(SN). Mating connector is JST PHR-2.
Many thanks! 
Thanks for asking, I had to look at mine and had me scratching my head too
One thing to look out for. If you are buying these connectors on eBay or similar, many sellers are selling what they call a "JST PH 1.25", which is too small. In theory, any two pin JST PH series connector (or clones thereof) should be compatible, but these are certainly not. I don't know whether they are actually selling GH series connectors under the wrong part number, or if this is some weird non-standard scaled down version of the PH series connectors. Make sure the listing specifies a 2 mm pin pitch and you'll be OK.
That you know, which it would be a good website to buy such batteries? Because I tried yesterday to search them most of the day from eBay and other websites, but I haven't found it, even on Amazon. My plan was to buy battery with connector already given, rather than only the connector.
I know Adafruit sells the batteries with the JST PH connector, but they are in New York, so they are shut down right now.
In your search, don't use the keyword "PH2". The "2" part refers to it being a 2 pin connector and that goes without saying on a battery. So look for ones that say they use the JST PH connector (but be aware of the issue I mentioned in my last reply).
I have a small collection of batteries I bought cheap on eBay and none of them use this connector, so it seems it is not the most common.
If you do decide to just get the connector and splice it to your existing battery, I recently purchased this listing:
https://www.ebay.com/itm/164069158129
They seem good enough. The first batch of JST PH connectors I bought on eBay were a very tight fit in the socket on my MKR boards, which made it difficult to disconnect the battery from the board. The connectors from the link above didn't have that problem.
Many thanks for the help!