I bought a 18v ryobi hedge trimmer it came with a p102 battery, I had 2 p103 batteries why won't the p103's work in my hedge trimmer?

Same problem here. I just purchased a Ryobi One + P320 nailer, and the fully charged P103 Riobi Li-Ion battery One + battery that works fine in my Ryobi One + P203 Cordless Drill will not work in the nailer. Its led lights just blink. Pressing its reset button in the hand per instructions fails to fix the problem. A supplement sheet in the nailer box lists P102 and P105 skipping P103. False advertising for "One +"? Now I have to spend over a $100 on a new charger and battery to get my Christmas present to work?

I do not know, but I have looked at generic battery versions as copies of those two and they seem one and the same in most respects.
So my thought is do they charge up? do they power anything else OK?
Then I would look at the contact areas to see if there is a difference like one has a longer contact or some bit of plastic is on one or not the other.
Many types I have found start out as specific, then over the years manufacturers sell out of older model types then decide to unify whats left to cover a slew of older models.
If charging is the issue then it is a real problem as these modern batteries require exact charging and if its controller finds a battery is below a safe charge up level point they become a brick.
Do not try to "fix" them as methods used on "tolerant" Nicad types to get them to work, is not safe on them they have a BAD reaction to overcharge situations.
If they are not that old maybe you can do a swap deal with Ryobi?

Hope this helps..........