Own a 2005 Toyota Sienna with 108,000 miles. Just installed L.E.D. lights all on the inside and outside. However I plan to drive all over the country soon and I will be replacing my original 17 years alternator. Since I plan to have GPS systems and phones plugged in while driving through the nights, bad weather using headlights, defrost Etc. Should I replace my old alternator with the same capacity or get a stronger one since I will be running a-lot of electricals?
no
Even manufacturers, when releasing car versions with more electronics inside, tend to also upgrade alternators. So in general it is a good idea to replace a stock one with a more powerful one, if your car has many aftermarket upgrades connected to its electrical system, to avoid battery undercharging (insufficient charging).
However it is useful to understand, that the benefits an alternator upgrade brings will only be noticeable to you if you mostly do short trips and idling. On the highway, almost any / even the stock alternator will provide (more than) sufficient power for all your car´s needs. It is at low RPMs that a stock alternator may be insufficient.
Another thing to consider is, that a more powerful alternator will handicap the engine more. And since your ECU will not be aware of the alternator swap (since I do not think that you will also do any ECU firmware modifications when doing the alternator upgrade), especially at low RPMs, an overpowered alternator may give you a rougher (fluctuating) idle, or, in extreme cases, even "adaptation out of range"-type errors.
On my old Audi, I had to do the alternator upgrade, since the car is full of all sorts of self-installed aftermarket options, and without this upgrade I could never get my battery charge properly. In my case, the swap resulted into more fluctuations when idling, but luckily no errors. However I would advise taking the risks, associated with such an upgrade, only if you are really experiencing problems with the stock alternator.
I always go for the high output, more beefy & it'll keep up with all of the insanity you want to plug in. I think the best autozone offer is 200amp.
GPS systems and phones plugged in while driving through the nights, bad weather using headlights, defrost Etc
millions of people are driving around with these things on right now, with their original alternator.
Small electronics are insignificant.