MXP:
Generally, dealers establish a trade-in value as the low end of the wholesale auctions values, and don't offer any consideration for things like a new battery (but may deduct if the battery is degraded). On the other hand, they will usually put a selling premium on the car if it does have a recently replaced traction battery. It's the nature of the business, buy low, sell high. A dealer will usually assume that you the customer have no insight into the wholesale values of your vehicle, and may try to lowball you even more depending on how well the car presents itself when you go to negotiate.
Everyone that I have talked to in the local community that have traded their 2011 LEAF for a 2018 have been reporting trade-in values of about $4K. The good thing is that values have bottomed out, and won't go much lower. Timing for obtaining a new car is also a consideration. You will get a better deal on a new 2018 if you wait till about August/September and the 2019 model year transition. You LEAFs will still be worth about the same at that time too.
You may want to consider selling your LEAF yourself, that may bring in an extra grand or so. Or you may want to keep them if they are serviceable and use them to generate rental income.
Keep in mind that the cars are almost 8 years old, and are entering the period that all cars go through where many of the soft items on the car like hoses, brakes, trim, and suspension pieces start to need replacement. Expect that you will end up spending at least a grand on general parts replacement in the next year or so for the car, assuming that a major assembly does not end up going bad.
If the carpool sticker is your primary concern you may want to reconsider that too, as even the carpool lanes here in the valley are jammed at drive time.
Hope this helps.