You may also be using 3.2V batteries that might fully charge to 3.7V but I doubt it and they would still work.
Do the batteries have 3.7V printed on the side of them?
Did you actually fully charge them (to 4.2V) before use as it is VERY doubtful they came fully charged.
Did you measure their voltage with an MTM (multimeter)?
Verified you soldered to the correct diode pins and correct board points?
Are the batteries actually connected to each other as in sometimes you need a spacer such as a small magnet between where the + and - are supposed to touch each other or else they won't make contact.
Is it built into a host or not? A very common issue is the clicky (on/off switch) on the host failing so you have to check with a MTM the resistance across the switch and verify it is actually closing.
Are you sure the host is conducting all the way through and to the module/driver if required?
We need clear pictures of things and some of these tests done otherwise I/we would just come up with a lot more questions than answers. We want to help you figure it out but there's just too many variables.
I will say that most situations like this the ending isn't good but there has also been plenty of surprising wins too
I've blown plenty of diodes and a few drivers in my time here from pushing diodes too hard and making really dumb mistakes in a moment of letting my mind wander away from a build.
By the way, I never put a build completely together in a host without first making sure it works without the host. It helps to cut down the troubleshooting time in case it doesn't fire up once it's all together.
