OP, this is the age-old question debated many times in other threads here since the 90kWh battery came out. I went with the 90 when I ordered and took delivery of my MS in October, but given a choice today, I would probably pass on the upgrade IF I WERE GIVEN A CHOICE to have the lesser-expensive 85kWh like it appears you have.
I tried to
write this up on my personal website in more detail a while back, but the net of that from my POV is:
- For $3K you get a little more than 16 extra rated range miles. That's a lot of money for some people -- perhaps not so for others that are more flush with cash.
- If you want only the best Tesla has to offer and can afford it, well, get the 90.
- Have you determined what the normal range is you REALLY NEED in your MS (e.g. to/from work each day and/or other regular routes you may take), including any additional buffers that help your mind overcome any range anxiety concerns, e.g. very cold weather, unexpected wind/rain/snow, the possibility you may have a much heavier foot than normal speed-wise or playing with performance features if you're MS will be so equipped, and any buffer for remaining kWh you want to have once you get home in case an emergency comes up before charging is complete (not as big of a deal if you have a 2nd vehicle, but could be if you are like me with only my MS now)? EVTripPlanner is what I'd recommend you do your modeling on, then add those buffers that apply to you to the range it calculates. From that, if the extra 16 miles a 90kWh battery covers your needs, well, that's your answer. If it's not really necessary, you have that answer too.
- If little things bug you, be aware that for some owners, the 90kWh Battery appears to have early degradation as reported by Rated Range compared to the 85kWh (beyond temperature swings, etc)... Tesla says this isn't a real problem, but only an issue with the way rated range is calculated and displayed, and it will be resolved in a future firmware release. We're coming up on 6 months since the 90kWh batteries came out and 3 major firmware releases have been delivered since then, and this problem hasn't yet been addressed. IMHO Tesla doesn't have the best track record resolving software bugs in a timely manner that are not associated with AutoPilot, so we could be holding our breath for a while wondering what is fact or not. Check THIS THREAD for the discussion and if you don't want to read all the banter, jump down to post #325 for a summary of exactly what Tesla told me this past December. Only you can then decide if this is or isn't a concern you should consider.
- Subjectively: The 85kWh battery is proven with 10's of thousands on the road around the world. Now that MX is out with the 90kWh as it's standard, Tesla IMHO has reduced the number of options because it's easier for them not having as many variations it needs to sell; Tesla has bumped the base price of MS up to include the 90kWh battery so that helps their unprofitable bottom line; More likely Tesla has something up their sleeve with the next battery size becoming available somewhere in the not-so-distant future so reducing the variations now makes that more sellable when it does indeed happen and Gigafactory comes online. Will a 90 offer better resale than an 85? Maybe. Everyone can debate all these subjective points all they want, but in the end, no one here knows any of it for a fact, so it all just becomes subjective input that may or may not sway you one way or the other. Personally, I'd try to come to a conclusion on the first 4 points I suggest, then let the subjective sway you if you remain on the fence.
Good luck with your decision.