2 questions: Difference between 65w and 90w AC adapter and 2nd battery

Hi, I'm about to purchase new inspiron 8600 and one thing has thown me
- the AC adapter. Dell offers two, One's listed as: AC adapter - 65w,
19.5v; the other as: AC adapter -90w, 19.5v [add $29]. My question is
what's the difference? Is one better than the other? (one would
assume there is a difference based on the price). Does one charge
more quickly?

Also, what are people's experience with using a second battery in the
modular bay? Worth it? (I like the idea of a little extra juice, but
I know these batteries tend to wear out quickly, so if it's only going
to add 20 minutes or power, I'll probably skip it).


Thanks.

 

The difference? 25 watts. heh. The 90W might come in handy if you do
have two dead batteries charging while running the computer flat out
with no power saving involved. I have a 2.6Ghz P4 15 inch screen Vaio
laptop. It has a 19.5V 5 amp adapter, i.e., 97.5 watts. The adapter is
barely warm to the touch under the heaviest load. My laptop has a 4
amp-hour battery that provides about 1.25 hours operation with no power
savings, which is representative of the normal power draw from the
adapter. That's equivalent to 3.2 amps load at 20 volts or 64 watts.
Adding a three-hour charge to the 4 amp-hour battery is another average
1.33 amps at 20 volts or 26 watts. Total (interestingly) 90 watts, just
below the 97.5 watt rating of the adapter.

Taking the same 4 amp-hour battery in a MPM providing perhaps 3 hours of
operating time is an average 1.33 amps at 20 volts, 26 watts for the
normal operating power, plus the charge on a battery over three hours,
26 watts or 52 watts total for the adapter. Add another battery
concurrently charging adds another 26 watts or 78 watts total.

So if you are going to charge two batteries concurrently while operating
the computer under normal conditions, the larger capacity adapter is
possibly necessary. Otherwise, the smaller adapter will work OK. You
can substitute your own estimates of how long your I8600 will operate on
battery to update the estimate I've made above.

Q