Is there a mod for slower need decay?

Yes. That mod is Relativity: https://www.nraas.net/community/Relativity

Once you have it installed click on any computer or city hall>NRaas>Relativity>Motive Decay Factors. The default setting is 1. That means the game's default. Lower than 1 is slower. Higher than 1 is faster.

Most people use Relativity to slow down the game speed itself: computer or city hall>NRaas>Relativity>Set Speed. The game default is 37. A lower number means the flow of time is slower in the game (but animations are the same). Need and skill decay is adjusted by the mod. Try half speed (19) for awhile to see the difference, then adjust as to your liking. Don't set the value above 37. By setting Set Speed to a lower number essentially it takes less sim-minutes for sim to accomplish tasks.

You can also adjust skill gain rates, the rate of need gain (Motive Delta in the mod), adjust skill gain to the life span your are using, etc.

@DivinylsFan Yes, you mean the Lifetime Rewards such as Dirt Defiant, Hardly Hungry, Meditative Trance Sleep, Carefree and Steel Bladder. The motive mobile will always fulfill all needs every time it is driven.
https://sims.fandom.com/wiki/Lifetime_reward

There's also a cheat to make all Sims happy and then put their needs on static. However, that makes the game pretty boring as Sims who are always content in needs don't seem to know what to do with themselves on high free-will in my personal experience. There's two ways to cheat motives. Ctrl+Shift+C brings up the cheats.
1. Type in testingcheatsenabled true in the cheat console, press enter and then freely drag the need bar(s) to the desired position.
2. Type in testingcheatsenabled true (if not done already) press enter and then shift-click the mailbox to make all happy and then make needs static which maxes out all Sims needs and then freezes it until you unfreeze by making needs dynamic. Or even make all happy without putting needs on static.

There is also some content in EP's or The Store that helps fulfill some needs quickly like the book o' spells, casting spells as a witch, Sharper Sim's Super Sleeper, The Not So Routine Machine, alchemy, The MultiTab 6000 raises social really quickly and helps kids and teens do homework quickly as well. I'm sure there is a lot more of in-game shortcuts depending on what is owned.

Motive depletion in TS3 is nothing compared to TS2 or especially TS. Oh, those games can be quite the struggle yet still fun but seriously the struggle for me is to not focus so much time on needs. :D However, I think they did an amazing job at balancing it in TS3. It's still relevant but not so much the focus. :mrgreen:

Relativity is one of my must-have mods. I never felt the speed of motive decay was unreasonable (I mean, they only need to eat once or twice a day, shower every couple days, and so on), but I always felt like it took too long for my Sims to do things and I couldn't get enough accomplished before bedtime. I set the time speed at 25, which is about 2/3 normal, and it's been perfect.

And then there's all the time savers @Deshong04 mentioned. The portability and rate of fun/social gain the Multitab tablet gives, along with the ability to passively raise skills while going about other business, makes it an absurdly useful time saver for the price. Those all-in-one bathrooms that max hygeine and bladder simultaneously are great too. My Sims also tend to end up with a bunch of dried food from their WA travels, and that stuff is instant hunger satisfaction wherever you happen to be standing.

The mod itself defaults to 0, which means Relativity is entirely "off." The game's default speed is 37. The speed being suggested is 19. I find that things happen a bit too fast there for my tastes, so prefer running it at 23 but the difference between that and 19 is pretty subtle (lower numbers make things happen faster relative to the game clock time). A negative value there would not be expected and I'm surprised it is even accepted. Values that are way too low, some say under 10 others say under 5, are likely to cause the game to trip over itself as time gets yanked back and forth and are not recommended.

On the Motive Decay/Delta settings, default is 1, slower decay/replenishment would be fractional values below 1 but above 0, faster decay/replenishment would be values above 1. Again, no negative values. Same with the optional skill gain deltas. (Edit: sorry, looks like I typed this part out backwards to begin with).

It's not over your head, but I think you have a slight math/logic fail going on there.

If you push a motive decay up to 10 (this is an absurdly high number, it's 10x faster than standard), then those motives will deplete astronomically fast. This is not generally recommended and thought I've already said that, sorry but maybe I wasn't forceful enough. What you are describing is exactly what is supposed to happen, your sims will need to relieve themselves or eat a meal 10-20 times per sim day. If you wanted faster motive decay, then start with 1.25 or 1.5, something like that, in very extreme circumstances maybe 2 but not 10. Note that 1.5 is already a 50% faster decay than 1, so 2 is twice as fast, etc.

If what you wanted was slower motive decay rather than a faster one, then it would be numbers less than 1, meaning fractions between 0 and 1 like 0.75 or 0.5. Just as with faster decay, there are numbers less than 1 below which things will never work right such as 0.001 (or somewhere around there, the mod cannot handle extremely small close to 0 numbers and at that point your sims would need to go to the bathroom every 500-1,000 days which seems a bit extreme in the other direction). Note that 0.5 is already 50% of a decay rate than 1.

If what you wanted was faster motive replenishment so that it takes less time doing something to replenish one's motives (like sleeping, bathing, or having fun), then that's motive delta not motive decay.

I actually have that already lol

didn't know you could do that thank you!

there is also the happiness rewards which you buy with happiness points that your sims get when they fulfill wishes

Hi guys, I need help with this Relativity mod. @TreyNutz said above that the default setting for game speed is 37, but i downloaded the mod yesterday and mine says the default is 0. I get that 1/2 of 37 is around 19, but how do you figure out whats 1/2 of 0 lol.

oh well, nobody answered and im tired of waiting, was hoping to have an answer before i played again, guess i'll have to figure it out for myself. hopefully using a - sign with a number will get me lower.

@MiSFiT203 Did you get it figured out? I think I'll get Relatively today too since I also want to slow time and mood decay slightly.