Output 42v 4amp is the same so in theory no problems. The only possible issue is how the charger "reads" the battery is full normally this is by a combination of voltage in the battery compared to input voltage so a full shimano battery might be 36.1v compared to a levo at 36.3v. The easy way to test this is fully charge both batteries (with their supplied chargers) and let them rest overnight then reconnect their original chargers to fully top up, rest them an hour or so and then plug in the opposite chargers to see if either battery takes any additional charge. Do this at the same time and both "should" indicate batteries are full but if one charger keeps trying to charge then you may have a problem so I would not use that charger on both batteries. You can also test the "full voltage" with a multimeter (more accurate than an app) to see if voltage is identical on both batteries. Overcharging is more of a problem than undercharging so use the charger which cuts out at the lower voltage and it should be good for both.