I too had some 15500s that seems like they had small power reserve. Like I'd take off the watch off after wearing all day at around 7 pm, and by 9 am the next day I saw tat the watch already died. Wearing them doesn't really charge them much either. The worst case was one that would die while being worn on my wrist lol. I've heard that it's probably because the movement is kind of dirty and need cleanup/service? I've had some serviced and it did make a big difference before/after. This seems like luck of the draw on the 15500s.
Big movement requires big rotor to charge. If movement is underoiled (often case with chinese movements) then friction is much higher, leading to lower PR. Get it properly lubricated and serviced and it'll run like a champ.
Both true. A few pointers on power reserve for the cal.4302 (and other movements in general)
1. The 4302 is a large caliber where watch movements go. The proper way to start it up (and I quote my AP SA) is to wind the crown until the second hand starts to run, and then another 20 winds. Giving it two shakes and then putting it on the wrist, will not be effective at all. Even the gen will stop on the wrist with insufficient wrist movement.
2. Wearing the watch alone will not charge it automatically. The key is wrist movement. A properly serviced watch does allow it to charge more efficiently both manually and automatically. This is especially true for the rep, which has a much lighter rotor (I am talking about rotational/oscillation weight) vs the gen. There is a reason the gen rotor is made of 22K gold and not steel. This allows the autocharging to be done more efficiently with each wrist movement. One inherent flaw or at least area of improvement in the rep is the rotor bearing assembly and rotor. They are often dirty and not greased properly, leading to unnecessary noise and stiff movements, which in turn inhibit the auto-charging of the mainspring.
3. The power reserve CAPACITY is determined properly NOT by wearing the watch an entire day, and then taking it off and seeing how long it runs, but a measurement of the period between the watch at maximum wind and when it stops. If the watch is worn for an entire day by a guy who is sedentary and lounging on his armchair, it is unlikely to have accumulated a nett positive charge. So if when he takes it off, and it stops say 3hrs later, the power reserve of the watch cannot be concluded to be 3hrs. If the watch is fully wound manually and then left alone, and it runs for 4hrs, for example, then there is an issue. And if the watch runs for 40hrs via manual wind and 3hrs if properly set up and worn on the wrist for an entire day with fairly active wrist movements, then there is likely an issue with the autocharging parts. So measuring the power reserve, especially of a large caliber, isn't that straightforward. Most owners will just jump to the conclusion that the watch is faulty, when it isn't really set up properly, isn't serviced to run optimally, or simply because there has not been enough wrist movement to continue powering the watch.
4. In general, smaller calibers will take less energy to keep running but will also have shorter power reserves. A lighter rotor will also suffice. If one can afford it and loves to wear the watch on a daily basis, consider investing in a movement service and a 22k rotor, as well as having the rotor bearing assembly cleaned and greased. This will allow the movement to run at almost, if not equal efficiency to the gen. The 4302 clone caliber isn't badly designed or manufactured at all. Like all mechanical movements, it has to respect the laws of physics and machinery and will need maintenance to run smoothly. I have measured the power reserve of a serviced sample (with the 22K rotor installed) to be at 72hrs before.
